Click a block to see what is under it. If it's a mine, you lose and all other mines will be revealed. If it's a number, the number will say how many mines are next to that space (including diagonals). If there's nothing under it, it means nothing next to it is a mine (including diagonals). If you know (or think) something is a mine, you can turn on flagging with the slider near the bottom of the screen. Clicking on something with flagging on will place a flag on it to help you remember that it is a mine. To win, flag all the mines and don't flag anything you don't need to.
Mines are selected at random, there is no fixed amount. I did not copy from anybody and all the sprites and backdrops were created by myself.
