Going to be posting a new homebrew soon.

I plan on posting a homebrew application on the Wiki soon. Thing is, I have no idea how. I haven't used Wikimedia before.

Could someone explain to me?

First off, sign up for a WiiBrew wiki account (not the same as WiiBrew forum account, you need both)
Then, go to the pages of a few different homebrew that are already on the Wiki, and press the "Edit this page" button at the top.
Look how each page is made up, and do yours in a similar way.

I can't really offer anymore guidance, but I'm sure if you post a wiki page, and ask someone nicely to tidy it up a little and make it look more like other wiki pages, they will oblige.

Thanks. I'll hopefully be posting it next week. I've still got a lot of work to do.