If you wad up a piece of paper and line up a shot at a wastebasket, you are taking aim. If instead, the paper bounces off your teacher's head, then your aim was way off.
A purpose or goal is an aim. When you were little, your aim might have been to be a famous astronaut, a movie star, or a police officer. As a verb, aim means to intend, try, or aspire. You may aim to take your dog for three walks every day, but your fenced-in yard tends to make both of you lazy.