Account has several related meanings that all connect to the idea of keeping track of something or explaining it:

When you give an account of what happened during recess, you're telling the story of events as you saw them. A witness might give an account of an accident to the police. Your account of the soccer game might differ from your friend's account because you each noticed different details.

An account can also be an arrangement for keeping track of money or information. Your family might have a bank account where money is deposited and withdrawn. When you open an email account, you create a place where your messages are stored and organized. A store might keep accounts of what inventory they have and what they've sold.

The phrase on account of means “because of.” School might be canceled on account of snow, or you might be late on account of missing the bus.

To account for something means to explain it or to be responsible for it. A teacher might ask students to account for their answers on a math test by explaining their reasoning. A scientist tries to account for unusual results in an experiment by figuring out what caused them.