Chilren playing on a playground
When Children are playing on a playground, this is free play. It teaches them to problem solve. For example, when they are doing something difficult for them, like monkey bars, they learn how to work through it.
It also teaches them to play and work with others. Often they have other kids to play with, and they learn to interact on their own without adults. They will often work together to solve difficulties, as in the monkey bar example