Here's some instructions since the game doesn't provide adequate instruction.
Match 3 of a kind and they will become the next type higher up, which you can see how they'll progress by the guide at the bottom of screen. You can see your next three bacteria in the upper-center area. Click anywhere on the board to place it.
Also along the bottom one of them will have some number(s) on it and this is how many of that type you must make to clear the stage.
Most are immobile but there is one mobile type. To change the mobile type to its next phase, prevent it moving for a turn. Once in the second phase, it behaves as per normal and is no longer mobile, match up 3 of these to get the next highest phase, etc...
You can also get powerups -- the skull and crossbones thing kills any of the cells along the white cell evolution line. However it levels-up any of the cells along the evolution line of the type where the lowest level is mobile.
There is also a copy powerup which, when placed next to cells, will randomly copy one of the cells but there are a couple of restrictions. It cannot copy the largest red and yellow cells which are the highest evolution of the small white cell type. It's best to make sure none but the cell you wish to copy is adjacent to the grid location you place this.
You get points by evolving bacteria and also by killing them off using the skull and crossbones powerup, strangely.
Spend your points in the shop to buy level 1, 2 or 3 of the white cell evolution line type, which replaces whatever was to be your very next bacteria type with that type.
Or you can also buy the skull and crossbones and copy powerups this way, which is what I recommend.
Additionally, at certain points in the game, you are given freebie skull and crossbones and/or copy powerups.
And for steps, every time you place a bacterium on the board that's a step. You also can get free steps by placing the copy powerup in grid locations the game doesn't accept, for example either where nothing is adjacent or only ineligible cells are adjacent (it can't copy the highest two types in the white cell evolution line). This does not use up your copy powerup. Hint hint - makes one of the medals easy.
And you lose if the board fills up and there are no moves available.
You also can optionally match up as many as you like, far beyond just 3, but 3 is the minimal and matching more won't give better evolutions -- they still just go to the very next evolution and you get one cell of that type, in the location of the last cell you placed of the previous type.
Cells match when they touch and are of the same type but it doesn't have to be in a row, just diagonals don't count as touching. So you could make any of the Tetris shapes for example, and it would count, and they would then all absorb and become one cell of the next evolved type and so forth.
I think that about covers it. So hopefully now this game is playable for those who were confused.