Think of the capo as a movable nut. If, without a capo, you play a G chord on the second and third frets, then with a capo you play the same shape on the second and third frets down from the capo.

So, if the capo is on the second fret, and you remove it, play the same shapes you were playing two frets toward the headstock.

The more experienced guys here can probably tell you more ways to use a capo too.

GG