Chord melody is a jazz style, usually for solo guitar. It can be picked but is usually played fingerstyle like classical or folk guitar. In short, one's playing all aspects of a tune oneself, melody, harmony, and bass.
How effective it is depends very greatly on one's skill, knowledge of music, ear, taste, and so on. How complex it is depends on one's knowledge of chord and note positions, harmony, and so forth.
It's not an easy style and some people never take to it. On the other hand it can be good fun to create a chord melody of one's own. You can do all kinds of things with it!
Just for fun here's 4 bars of a tune with very basic harmonies followed by the same tune jazzed up, chord melody style.