To start, left click any tile on the board. It is generally recommeneded that you always start in a corner to get the best start possbile, but in my example I started in the middle, it should also be noted that each game of Minesweeper is random, and yours will never look like the example game I have shown.
The number that appears is the number of mines directly adjacent to the tile that the number is in. In this example, the 8 adjacent tiles around the 1 tile, must contain 1 mine. The number of mines on the board are located on a counter in the top left.