Answer: An understandable question. Chord notation in the form G/B could easily give you the idea that you have your choice of playing G, or alternatively B if it suits your mood. But actually this refers to a G major chord, and the B after the slash tells you that the B of the chord should be the bass.

In terms that would be understood in a music theory class, this is a first-inversion major triad, a triad with its third (the middle note) in the bass. The order of the upper notes doesn't matter, but the bass must be B, and the other pitches will be G and D.