Alternator belt installation

If it is this one it looks like a common screw style adjuster. Basically you need to loosen the mounting bolts for the accessories. Back the screw adjuster off, install the new belt and use the screw to tension it. They want you to use a belt tension gauge. If you do not have one many parts store rent/loan tools.
Tighten the belts to the specified amounts. Tighten the mounting bolts down and recheck the tension. If it reads right you back the tensioner off and lock it in place.

Using new belts =
Alternator - 140-180 lbs
Power Steering and A/C - 140-180

You will find versions of them on a lot of vehicles that do not use automatic tensioners with the belts.