The handle functions as an on/off switch. You should always tighten it until it stops and then back off until the handle is parallel with the a frame. Doing it this way will ensure that you always get the same amount of tension on the bar - no guessing. :)
The adjustment is the small bolt with the hex head on it below the bar. This should be preadjusted from the factory and, in most cases, does not need to be changed until many miles of towing have passed. Of course, if you have a very light or small trailer then you might have to make an adjustment. The advice given in the post above is a good way to do it.
Barney