As far as what to put in it I'd go to the LFS
and see what you like. Come home and do some research about what their temperament is, suitable tank mates and what water parameters they need [some fish like guppies and mollys like brackish water, some fish prefer high or low ph, etc]
You can Google any fish and just add the word "care" after it and you'll get specs with everything you need to know.
You can post here, too. Pick a fish and post a thread asking what gets along with it, what kind of food it eats...all kinds of good stuff. I'll tell ya-you can find someone here with experience keeping just about any kind of fish you can think of.
I know it seems like we all came down on you, but only because we have probably all made the mistake of getting a tank and throwing fish in right away. There's an easy way and a hard way. Add fish too soon and you'll spend the first two months worrying about the fish, checking water parameters and doing daily water changes and that kinda takes all the fun out of it.