Guitar action refers to the distance between the strings and the fretboard. Lowering the action can make the guitar easier to play, especially for beginners, and can improve the overall sound of the instrument.
There are two main ways to lower the action on a guitar: by adjusting the truss rod or by sanding down the saddle. The truss rod is a metal rod that runs through the neck of the guitar, and adjusting it can change the curvature of the neck. Sanding down the saddle, which is the small piece of bone or plastic that sits under the strings at the bridge, can also lower the action.