A comb is a tool for smoothing your hair. You might pull a comb through your curls before you run out the door in the morning to catch your bus.
A comb is made of plastic or wood, with separate teeth that untangle strands of hair. When you use one, you comb: "I grabbed the comb so I could comb my cat before the photo shoot." Another way to comb is to rummage or search, the way you comb through your bag to find your car keys. The Old English root is camb, "crest" or "honeycomb," from a Germanic root that means "toothed object."