A string winder consists of a rectangular socket attached to a handle on a swivel. Once you attach the string properly, the socket goes over the nut that winds the string being tightened. Once the socket is over the nut, the user merely rotates the handle in the direction needed to tighten the string - the winder merely acts as a method for accelerating the nut winding process, since you can turn the nut faster with the winder than you can with your fingers.
Winders are only meant to take up the majority of the string slack - once it gets fairly tight, it should be taken off and the rest of the string tuning done by hand. Use your fingers to tighten the nut to concert scale tuning, and make sure you tighten the nut screw. It's always a good idea once you've tuned all the strings once to go back around again and check them once more, as tightening strings always tends to loosen others already tuned by a little bit. At a certain point they'll all be tightened to the same relative tension and you won't have to deal with any loosening as you tighten all of them.
Pack of 10