Australian football, or “footy”, as it is known (the ball is also often referred to as the footy), is played on a large oval field (135-185 meters long from goal to goal, and 110-115 meters wide) and has four large goalposts on each side of the field. Points are scored by kicking goals, which occurs when the football is kicked between the 2 middle goalposts, and behinds, when the ball is kicked through the outside goalposts. Goals are worth 6 points and behinds are worth 1 point. There are 18 players on each side, with 3 interchange (bench) players and 1 substitute on the side. The ball can be disposed of either by kicking or handballing (bumping the ball with the fist, similar to volleyball), and goals can only be scored by kicking the ball through the goalposts.
There are many more technical rules, which are explained in the following two videos. The first video provides a quick 7 minute summary of the basics of the game. If you have some extra time, the second video provides a full in depth explanation and is approximately 30 minutes in length (recommend to watch only up to the 14 minute mark for game-specific information).