Trapper is one of the two job options you have available to you at the beginning of the game, they are assigned to hunting zones and traps game to get meat(e.g. rabbit jerky) and fur pelts. At level 2 they begin to befriend some of the captive animals and may convert them to pets.
Lv 1 - 10% movement speed boost
Lv 2 - Befriend captive animals and convert them to pets.
Lv 3 - Helps salvage more from each animal
Can be retrained into shepherd
Lv 4 - 8 room increase in backpack, makes the rounds more effective
Lv 5 - Traps are allowed to capture larger prey
Lv 6 - Traps detect nearby animals, increases rate of catching
Guide: It is not recommended to get a trapper as soon as you start despite having that option, since trappers will constantly check their traps they almost never help with harvesting or building. Trappers should be trained when your settlement becomes "Self-Sufficient" and you want that extra happiness from meat.