If it's within 4 hours, there is an edit button on the bottom of your post, along with the other buttons (quote, reply, report this post, and ignore user). After that button disappears you can't edit your post anymore, but you can still use the "report this post button" and ask them to delete your post, then post a new post. You might also try using the "report this post" button and tell them you want to edit the post, but I have never tried that. I have done the delete and replace though.  
 
Since you are new, your posts are moderated so they will take a little time before they post. Any edits will also be moderated. After posting a while, you can ask to be unmoderated and your posts and edits will go up instantly.  
 
Good luc