When installing an electrical outlet, there are two ways to attach the wires to the outlet.
One method is to back wire the electrical outlet. But side wiring is considered to be the "classic" technique for attaching the wire, if only because this is the original method. Side wiring does have its advantages, chief being that it tends to grip the wires a bit tighter.
First step is to loosen the screw without removing it. I've never been that adept, and often the screw pops out. Not to worry. It's not easy to get the screw back in, but it can be done.

