Can someone ELI5 op amp gain?

I'm trying to figure out how feedback is changed in closed loop for op amps in inverting and non inverting configurations.

I know some of the basics: non inverting gain is always positive (equal to or greater than 1); I'm not sure how inverting gain works, i.e. can it be negative, or simply less than 1?

Is unity gain the same as a voltage follower?

What other basic principles should I know?