Need help finding the alternator belt tensioner

I figure the hellish screeching coming from under my hood is my alternator belt, as it stops after 20-30 seconds and the battery is getting sluggish quickly. Problem is, being an idiot who still wishes to save money, I don't know where the tensioner is on my 93 Nissan pickup. It's been going on for a while so the belt pulleys may have polished the underside of the belt by now, but I want to try tightening it before I hand out cash to get the belt replaced. My mechanical inclinations extend to where the key goes and where the gas nozzle goes and, well that's about it. I am a whiz at presetting radio stations but that has nothing to do with my problem. Simple steps would be appreciated. Thanks