You have bought a baitrunner. Its a nice looking carp reel. This reel has a twin drag feature (baitrunner) and is popular with carp anglers. I use a baitrunner as well only its a multiplier. The principle is the same.
On your reel you can set your primary drag using the knob that's located above your spool. This sets the drag on your reel, set it to roughly one third the breaking strain of your line. You then throw the lever that's located on the top of your reel. This disengages your primary drag. You can now adjust the knob at the rear of the reel, primarily to see you don't get an over run when a fish hits your bait hard. Also when your baitrunner is on you will hear a loud clicking sound as line moves out of your reel. The idea is to let the fish pick up the bait and move on with out feeling any restriction from the line. By turning the handle on your reel the baitrunner disengages, the pressure comes on and you hook your fish to fight it on your primary drag.
I hope this clears things up. These reels are a boon to use when bites are slow. I'd suggest you invest in a rod stand so you can have your rod in the stand, baitrunner on and your hands are free to scratch your head and wonder when you'll get your next bite