To start out making a champion, you can either make a sandbox (creating a page on the wiki with "User:Nomedhexcube/Sandbox" as its name) or use an off-wiki document. Posting of such champions should be done as a blog. Do not post WIP blogs though, as blogs should be mostly finished products, ready for proper review.
FYI, some of these were mentioned in the guide I linked you to. Please read through the instructions. If you do have a question, please be more descriptive or at least add more content, or else your questions will sound like "I only skimmed, but question."