Heres a creatine guide. It should answer all the questions you have
http://www.askscooby.com/nutrition-39/creatine-faq/As for whether or not you need creatine, I would say no. It gives you some extra reps and a little bit more strength which is good, but its really up to you do decide if 1-2 extra reps is worth spending your money. I may try it some time in the future when my muscle gains slow down.
As for what brand, I have only tried products from optimum nutrition and prolabs. They both also have lines of creatine so go ahead and try one of the two. Also make sure to get the creatine monohydrate.