Slide tiles around and try to make a row or collaum that's all 1 cookie (the board is 5x5 so it will be 5 cookies). That causes a clear which will give you a point and then 5 new cookies. Then new cookies are random but 1 will be a yoshi cookie. After a clear if there's then a row/collum that is newly full (the board will be 4x5 assuming 1 clear, meaning this second clear can be with 4 cookies) it will clear, give 1 more point, and will make the new cookies contain 5 yoshi cookies instead of just 1. Chains can keep going after that, but you will always get 5 yoshi cookies from a chain, never more. When you clear Yoshi cookies it will give a point, activate whatever special move is selected, and spawn 5 new cookies. The new cookies will not conatain any yoshi cookies. If a yoshi cookie is part of a chain that chain will give 1 yoshi cookie instead of 5. Chaining Yoshi cookies also allows you to make special move attacks while only using 4 yoshi cookies. There is also a timer, called the fuse, that will reset after each clear. If the fuse runs out then you die. The fuse lasts for 25.33, 20, or 14.67 seconds depending on if the game is set to low/med/high speed for mario, peach, and yoshi. The fuse lasts 13.33, 10.67, and 8 seconds depending on if the game is set to low/med/high speed for bowser. After moving a piece there's a small animation that plays of the cookie moving into place. It lasts 13 frames and during that time you cannot make other moves. The board is 5x5, which means you have 25 cookies, and there are 6 possible cookies. That means mathmatically you must have at least 5 of one kind of cookie at any given time, however you may only have 1 cookie that has 5 and that may be a yoshi cookie. Since the specials are random it is possible that you get stuck with a bad special and have to either waste the yoshi cookies on it, or wait out the cycle and hope for a better special (known as overbaking).
There are 5 special attacks, +/-3 points, Panic, Blind, Slave, and +/-7. Each are equally likely except for +/-7, which are more rare. the +/- point abilities just add or remove points. The others all last for a set period of time. Panic renders the target unable to control their board and randomly re-aranges the tiles. Blind obscures the center 9 tiles. And Slave gives the user control of the target's board. All attacks can target either the player or opponent. The player character will be happy, sad, or neutral to show if the attack is positive, negative, or neutral. The only neutral attack is self slave which does nothing. Also it is important to remember that clearing a yoshi cookie gives you a point, and then applies the effect. This means you will win the game if you clear a yoshi cookie as your 25th point, even if the effect would either prevent you from winning or cause your opponent to win (such as a -3 or +3). One weird quirk is that if you are slaved and you make a yoshi cookie clear that applies it's effect as you are losing control, you will cancel out the slave. I'm not entirely clear on if this happens with all specials or just some, but I've gotten it to work with a self targeting +3 so at the very least that should work.
Some common uses of special moves include: Prioritizing + and - 3s in order to get ahead on points, Prioritizing Slaves and Panics to prevent your opponent from being able to play, Using a Slave and then making a YoCo clear on your opponent's board to do some kind of bad effect for them and prevent them from having the cookies avalible to attack you.
All characters have 4 stats, Attack, Defense, Limit, and Message. Attack is a modifier that makes Blind, Panic, and Slave last longer. All characters have the same attack except for bowser who has high attack. Defense is a modifier that makes Blind, Panic, and Slave shorter. Peach has Low Defense, Mario and Bowser have medium defense, and Yoshi has high defense. Limit is how long your fuse is. All characters have the same Limit except for bowser whose limit is shorter. Message is the speed at which the randomly selected special move cycles. Peach has short cycles, Mario and Bowser have medium cycles, and Yoshi has long cycles.
Mario has no strengths and no weaknesses, he is the definition of boring and it's impossible to say if he's good or not (just kidding, he sucks). As a character choice Yoshi outclasses him in basically every way since yoshi also doesn't have any real weaknesses. The only upside to mario is a shorter cycle which isn't better really, it's just different and mario's cycle isn't really short enough to make a huge difference in playstyle vs yoshi. With 5 second cycles and a 20 second timer (med speed) mario can technically wait out 4 cycles but in practice it's more like 3.5
Peach has low defense which leads to her getting comboed to death sometimes (especially against bowser). Having the short special cycle means that she is less dependent on RNG for getting good attacks by virtue of having more chances to get a good special. Her cycles are 3 seconds long, so on a medium speed game where her fuse is 20 seconds long she can hold out for 6 cycles in a worst case senerio. This makes it easier not only for peach to not get stuck overbaked in RNG hell, but also that she can afford to wait it out for a specific special. The shorter message speed can also make it harder to react to a good special however, so it's a bit of give and take. As a character choice Peach is interesting, she's both less and more volitile. Peach vs Bowser is very very scary since 1 panic from bowser will lock peach out of the game for 21 seconds. She tends to do alright vs Yoshi since she will most likely get more chances for point manipulation, but is still suseptable to yoshi stunlocking her via Panics and Slaves. She's kind of a glass cannon where if you're fast enough to properly capitalize on the strengths of her fast cycles you can launch a more consistent, controlled offense, but if your opponent gets the upper hand early they can give you a big mountain to climb.
Yoshi's high defense means that they're not really all that bothered by Panic or Slave, and then because their attack is just as good as mario/peach it means that yoshi isn't any less dangerous. Having the slower message cycle does mean that it's easier to overbake with Yoshi, but it also means they have plenty of time to capitalize on good cycles. Also with such high defense it means that Yoshi isn't as bothered by taking a self blind or panic to get new cookies & reset the cycle as bowser or peach would be. With an 8 second cycle and 20 second timer (med speed) yoshi can wait out 2 cycles. Yoshi has no real downsides, he's more likely to overbake but also has the tools to deal with overbaking better than any other character, so it more or less evens out. He's basically the ultimate low risk character and is a good choice for beginners who are maybe worried about playing too slow to take advantage of peach or bowser's strengths.
Bowser has high attack and low limit, his panics, slaves, and blinds last for a really long time and if he gets the right RNG he can loop attacks back to back and never let the opponent play. In exchange for this his limit is lower which both restricts how many cycles he can wait out as well as being a bit more threatened by fuse pressure. Bowser has 5 second cycles and a 10.67 second long fuse, which lets him only wait out 2 cycles. In theory this is the same as yoshi, however bowswer has way less time to act if he chooses to wait those cycles out, .67 seconds vs 4 seconds to make a clear and not immediately lose the round. Also, bowser's high attack and average defense make self attacks hurt more than yoshi. 14 seconds for a self attack from bowser vs 3.5 seconds for a self attack from yoshi. Bowser's fuse can also be an issue if he gets paniced just before making a clear, especially if he took extra time to setup a chain. Since panics scramble the board and don't reset fuse bowser might wind up with only a second or so to make a clear, this is less of an issue at low speed and even more of a problem at high speeds, on medium speed it's more of a situational thing. All that being said, the lower limit does not matter for most of the game, as it's usually more than enough time to make clears and even setup chains, it's only an issue if the bowser player has screwed up by overbaking or goes really far out of his way to setup a chain. The reward for playing bowser also more than makes up for this fault. Bowser is really the only character able to scare Yoshi with attacks, lasting 7 seconds. It isn't as much as bowser gets on the other characters but it's significant enough to matter. 21 seconds of panic/slave on peach is also incredibly strong, if you are able to make 1 chain every 3 seconds that peach is out of the game, which is not really out of the question, that is as good as a +7, better actually since that would leave you with 7 yoshi cookies for you to use potentially on another Panic or Blind. As a character choice bowser is a very good pick for players who want to rely on panics and slaves. He has a bit more of a skill floor since not properly covering for his faults results in immediate round loss rather than just suboptimal play, but it isn't too high a bar to reach once you understand the mechanics of the game.