As soon as you create your poetry, the copyright is automatically yours. You don't have to do any more (although people often do - belt and braces and all that). Putting it onto a website can actually strengthen your copyright, because then there's a digital time stamp on it that you can use in the event of any legal proceedings.
If you're worried about posting it here specifically (or if you're not allowed to), you could join one of the many writing forums on the internet and post your work there. Then you could simply post a link here if you wanted others to go and look at your poems.
I can thoroughly recommend Writers Dock (
http://www.writersdock.org ) and More Writing (
http://www.morewriting.co.uk/ ) for starters.