Crab pots can be crafted, or purchased for 1500 gold at at Willy's Fish Shop once you've reached a sufficient fishing skill level.
They are very useful for increasing your fishing level without actually having to fish.
Fish caught with the Crab Pots (Lobsters, crabs, etc) also count towards the Mother Catch Achievement.
Crab pots are floated on the shores of bodies of water (lakes, streams, or oceans) and primed with Bait. Players with the Luremaster profession doesn't need to refill the pots with bait.
The next day, the following items can be obtained: