This is probably the hardest thing to explain. But here goes:
First, check your maintenance manual. I've not checked my Legend manual, but on my other Hondas, there is a procedure for checking belt tightness using a ruler, a weight, and a raw chicken. Next put the manual back down as I find it useless in this situation.
If the belt is loose enough and has been making noise for some time, there are signs you may see on the belt itself. If it is glazed (very shiny), damaged etc. this could indicate a problem. If you find a damaged belt, replace it. You may never get it to stop squeeling.
I just tighten and go by feel. Not too loose, not too tight. You should be able to bow the belt some with moderate pressure.
Here's the twist, you don't want the belts too tight as you can damage bearings in the alternator, A/C and power steering pump. If you think it could be a belt, just tighten them one by one a tad and see if anything changes.
Good Luck!
Dave