Brie, Kathymack or someone else with more experience will be able to explain it better, but basically an apple cider vinegar rinse helps balance out the PH in the hair. It helps if the hair has a good balance of PH and acid.
You aren't washing in pure vinegar, you're rinsing in a diluted solution of vinegar. I tried rinsing in a plain white vinegar solution once when I was out of ACV, and it works ok, but ACV works better. Must be the apple cider content.
Check out the newbie forum, and the homemade recipes forum. There are lots of good ideas there. And check out the swap board, that's a good way to try out products without commiting alot of money to buying them.