In the following example, you will notice some new chord symbols. These symbols indicate a chord with a specific bass note under it, and are called slash chords. E.g. in bar 2, the chord symbol G/B occurs. This indicates a G chord played over a B bass note.
In bar 4, the symbol G/D indicates a G chord over a D bass note. In bar 5, the symbol Am/E indicates an A minor chord with an E bass note. Slash chords are often used to create smooth, melodic bass lines and the symbols tell you that a note other than the root is played as the bass note of the chord.