You insert the non-stripped wire into the hole onto the spike at the bottom. Screw in the ring around the wire and it creates tension on the nylon inserts to hold it in place. It's a VERY strong connection; I can't even come close to pulling it out. There are holes on the outside of the screw-in rings so you can torque them down with "something", I bought this used so I'm not sure if there's supposed to be a special tool or what. Hand tight is plenty, or you can use some pliers.
Accommodates (2) 8AWG, (1) 4AWG, and (1) 0/1AWG (Also includes a 4AWG to 0/1AWG adapter which you can see in this pictures)