If you have problems understanding the Sally-Anne false belief example, try this one instead.
You and a friend, Kelly, drive to the shops in your car. You park your car in a particular street (Mount Street) and as you both have different shops to visit you arrange to meet back at the car in an hour’s time.
Shortly after parting from your friend, you realize you have left your wallet at home, so you take the car home to fetch it. When you get back to where you parked before, the car park is full up, so you have to park in a different street (Park Street).
You know that when Kelly goes to meet you she will assume that the car is where you originally parked it. Unless you can find her first, she will go to meet you in Mount Street, not in Park Street. In this situation you understand that Kelly’s belief about the location of the car is false, and that she will act on the basis of this false belief.