On each side of the crank you should have a bearing cup, and on one or both side(s) a locking ring.
The outer locking ring(or nut) is what locks the bearing cup in place. Once the cups are set, I lock mine with a screwdriver and some good whacks with a hammer. Remembering that the left side is a left hand thread(!)
Snug up the cup first, then lock it down good, being careful the cup doesn't tighten too much to bind up the bearings while hammering.
That's all there is to it.