Move the key without learning new chord shapes

Capos

A capo clamps across a fret and shortens every string at once, so the shapes you already know come out in a different key. That makes it the fastest way for a beginner to play along with a recording. The thing that separates a good one from a bad one is whether it pulls the strings sharp: too much clamping force bends the string sideways and the guitar goes out of tune.