A:
Trot lines are made to be stretched over a wide area (usually from a tree or downed log to another anchoring point). The line is usally baited with cut shad, bluegill, worms, or even liver depending on the species of catfish that are targeted and what works best in your area.
As well the line will need to be anchored by a large enough weight to keep the line on bottom. As well, you may want to tie a jug to the line to help mark where the line is (and to keep boaters from chopping the line up in their props).
As for catching the catfish, when a catfish does take the bait, they tend to hook themselves due to their actions. Just be sure to check the line often to ensure that the hooks are baited and that no turtles are eating the bait or fish that are caught.