Info on good cameras please?

[Emma]

I'm 15 and I'm thinking of going into photography but first I need to get a good camera because right now I only have a small digital carry around nikon (12 megapixels).
I'd like to get a good Canon but I can only afford up to max 500 dollars. Also could someone explain the importance of megapixels? because I know that they affect the quality of the pictures but is that all? I have seen Canons in my price range with 18 megapixels, is that a good amount? What should I be looking for in a camera? My uncle who is a photographer also told me that the lenses are one of the most important part. He said that the Pro L lens Canon series is really good but how much do they cost and which ones should I get? Could someone please give me some advice on which Canon models I should be looking at which are not too expensive and are for beginners?

Thanks