A special tool is inserted down the axletube to adjust gear backlash and bearing preload. Tighten each ring adjuster for a tad of preload on the bearings, then use them to move the ring gear closer or farther away from the pinion gear to obtain the correct backlash, usually 0.004-0.007 inch as measured with the dial indicator. Paint the teeth with marking compound and verify that the pattern is acceptable for smooth and quiet operation. Tighten up the side adjusters for proper bearing preload, and insert the lock plates to finish it off. If you aren't familiar with this process, you might want a professional to dial this stuff in.