In baseball there is 9 innings. Each inning has a top and a bottom. The top of the inning is where the away team bats until 3 outs are made. The bottom of the inning is where the home team bats until 3 outs are made. It continues this way till the 9th where if the home team is winning, and 3 outs are made in the top half, the game is over. If the away team is winning, the home team bats in the bottom of the 9th to try to tie the game or win. If the game is tied after the 9th, it goes into extra inning.
Extra innings is where you play innings until someone scores a run or more. If the away team scores in the top half of an extra inning, the home team has the bottom half of that inning to score. If they don't, the game is over. If the home team breaks a tie in the bottom of an extra inning, they win. This is called a walk-off. There have been walk-off homeruns, 1b's, 2b's, 3b's, hit by pitchs, hell even a walk-off walk.
Anyway, hope that helped. And yes, I do play baseball. Back in high school and for fun.