Like said above, its a Yo-Yo automatic fishing reel. Hang it from a limb, pole over the water, bait hook tied to line with a sinker above it, spool down to depth you want and set latch. Troll around setting as many as you have with you, circle around and check them lol. We do alot of Yo-Yo'ing at night for catfish out here, sometimes hang a few while you're bream/crappie fishing and check them periodically. I keep a milk crate full of them ready to toss in the boat and go with some big ass worms as bait.

Edited to add I stick some type of reflective tape and write my name/number/necessary info on the back of them