Syutbai explained it well. However another better understanding of it is that 'percentages' is used in mathematical situations, though it still has the same rule or rather meaning of 'per hundred'. Percent can be identified as being one part in a hundred. and more or less i suppose it used in the business industry and mathematical terms as well. such as "The employment rate increased to 1 percent this year." Overall both words are exactly the same. You can use either of them in a sentence depending on what your sentence is.

Merci Sophie

si tu veux, je vais t'aider. I used to speak french but it's been 8 years since i haven't spoken it, so i've lost the ability to make good meaningful sentences if that makes sense...anyways, despite that fact, i am still quite good (in fact excellent) with my pronounciation. so if you want you can just write the words you want to pronounce and i can help you pronounce. P.S. I can also understand french perfectly, it's just my writting and sentense formation that's affected LOL (weird huh?! :P)

je pense pas que la grammaire 'uh' a francais et dificile...mais c'est different at tout le monde j'espere...hmm oui, la grammaire et difficile a certains mon... as you can see my french isn't all that great but yeah...i think i explained myself a bit okay...