Slash chords are basic open chords, which are made fuller by adding a different root note (ie. the lowest note in a chord). For example, if you played the C chord and wanted G as your root note, it would be called C/G. This is a slash chord. The first letter is the chord you play and the second letter is the root note. Here is how the C/G chord is played, showing G as the root note...

e|------0------| B|------1------| G|------0------| D|------2------| A|------3------| E|------3------|

Another example of a slash chord is D/F#. This is much more tricky. This means play the D chord with F# as the root note. Here is the chord in tab...

e|------2------| B|------3------| G|------2------| D|------0------| A|-------------| E|------2------|

When playing this chord, all your fingers are used making the D chord so in order to play the low F# you need to use your thumb. To do this play the D chord as normal and hook your thumb over the neck and use it to fret the 2nd fret of the low E string. This may be difficult but practise makes perfect!

Here are some more for you to try out yourself:
· A/C#
· Em/G
· F/C

If you get stuck, you can refer to the chord library for help!