The amount that you tighten the castle nut determines the pre-load. There is a flat washer between it and the bearing. You install the bearing, washer, nut, then tighten the nut to 20 ft-lbs, then back off 1/4 turn, then finger-tighten the nut. Install the collar over the nut and the cotter pin. To check if it's tight enough, install the tire and grab it 180 degrees apart with both hands while elevated, and try to wobble the tire. There should be no play.
If it's too tight, which a mechanic did to me without my knowledge, it will burn out within about 5,000 miles. It will start making a low-pitch roar like a jet, at speeds around 45 mph, and as it starts to seize, will be louder at lower speeds. When I pulled the drum, the bearing had welded itself to the spindle. I had to get a Dremel tool and cutoff disc and cut the bearing collar away, tumble out the needle bearings, and pry the inner collar off the spindle after nicking into it with the cutoff wheel. The spindle fortunately had just started to burnish, did not have to be replaced or resurfaced.