Beginner guitarists are often confused when they find a slash chord. The good part is that they are easy to understand.
The purpose of slash chords is to specify when the lowest pitch in a chord is not the root note. Often we call this the bass note even though a bass guitar is not playing it. For example, G/B is a G chord with a B as a bass note. When spoken, we call this G-slash-B or G-over-B.
The example below shows three examples of slash chords based on the open chord grips for G, D, and A.