Funk guitar is defined by a percussive and often muted rhythmic sound. Chords and melodies are rare, and riffs, when they exist, are simple.
This percussive, rhythmic way of playing might be tricky to get a hang of. It involves a lot of muting with your fretting hand and requires some speed.
The best way of learning how to play funk guitar is by listening to funk and learning the guitar parts of those melodies. Although diverse, many songs feature similar guitar rhythms.
While chords are rare in funk music, chord positions are not. The fingers are placed on the fretboard as if you were playing a chord, but instead of hitting every note at the same time, you only hit one or two.
The 9th and the 13th chord are two popular chord positions in funk music. Yet, as with everything in music, it varies from song to song.