The difference between prepaid expenses and unearned revenue

Prepaid expense means you paid for something that is an expense before it is used. It is a current asset.
An example is: Prepaid Insurance = you pay insurance for a period of one year or longer. As the insurance is used it transfers from prepaid insurance to insurance expense.

Unearned Revenue is a current liability. This means that you received money for a service or something tangible and you have to provide the service or something tangible.
An example is a magazine subscription or an advance payment for consulting fees.
The company that receives the money will record the money received as Unearned Revenue, then as they the provide the service or tangible goods then they will transfer the amount of revenue that is now earned to Earned Revenue.