Absolutely what Sam V. says.
The end-float screw should be backed off a tiny bit so there's just a perceptible bit of in-out travel along the axis of the spindle; it should never be used as a brake.
As to the Compensating or Micro-Drag, you'll see two spokes, opposite each other, are "special". Each has a "U"-shaped prong at the end, which runs in the narrowed portion of the tip of the pin.
The one with the plain barrel is the spool release; pull the barrel out along the spoke, away from the hub, and the spool can be released.
The other, with the knurled wheel, is the drag, which can be loosened off to let the reel spin as freely as possible; applied gently to give a constant drag when holding-back in a strong flow; or set at a point where the spool doesn't pay off yards of tangle-hungry slack every time you lay the rod down - particularly handy when fishing still waters.
lt's also useful if you're using the reel as an intermediary line-holder in the job of reversing a carefully loaded fixed-spool's shot of reel line plus backing.