AFL pitches are massive - much bigger than a football (soccer) pitch. They are usually shared with cricket grounds, which is why they are shaped like an oval. The ball is shaped like a rugby ball but a bit bigger. Players run, bounce the ball, pass it with their hands, and kick it to teammates.
The most exciting thing in AFL is the 'mark'. When a player kicks the ball a long way through the air, anyone who catches it cleanly - sometimes by jumping up onto another player's shoulders - is awarded a 'mark' and gets a free kick. These leaping catches are spectacular, and the crowd goes wild.
There are six posts at each end of the pitch. Kicking the ball cleanly between the two tall middle posts scores six points - a 'goal'. Kicking it between a tall and a short post scores just one point - a 'behind'. A typical game might finish with scores like 105 to 92, which sounds huge but makes sense when you can score so many ways.
AFL season ends each year with the Grand Final, held at the Melbourne Cricket Ground. Almost the whole country watches. Schools, neighbourhoods and whole families pick a team and stick with them for life. Many Aussies say AFL is more than a game - it's part of who they are.