design_mom explained it upthread, but basically, you're given a box on a grid with 0-9 randomly assigned on the top and side of the grid. If the numbers you have (say, 1 for the home team and 4 for the visitors) is the score at the end of a quarter or the end of the game, you win. So, given the numbers I mentioned, the final score of the game was 21-14, you'd win,
Most of the ones that I've played give a smaller amount for the 1st, 2nd and 3rd quarter and the largest prize for the end of the game totals. Most groups that do it for fundraiser will keep 1/2 for the organization and 1/2 for prizes, so if there's $100 collected ($1 a square), $50 goes back to those who bought squares and $50 goes to the charity / organization.