To trap an animal, either kennel or Butcher's shop and dd the 'Capture live land animal' task, or - build an animal trap, which must then be baited with meat or fish. Many vermin animals are tamable and can be tamed at the kennel.uery a
Trappers will pursue and catch tame vermin that's outside of a container.
The trapper skill is also used in creating animal traps at the carpentry workshop, a metalsmith's forge, or a magma forge.
Trappers can be used to control the vermin population and/or acquire fancy creatures to put in cages and place in your fortress. In the first function, they are easily outperformed by cats, and the second is mainly attractive if you feel particularly elfy. As one of the Ranger professions, they sometimes come with more useful skills such as marksdwarf or ambusher.