A wiki is basicly a system that allows for a group of people to create a website together; meaning that everybody can edit the pages and add new pages. So this way everybody can sign up and help out. If you want to add some information to the wiki pages just hit "edit" and you'll be allowed to change the page. If you want to make a new page you have to create a link to it from another page by adding (to a page that already exists): [[MP3]]
Then there will appear a MP3 link (underlines as normal links but marked in red to show that the page does not yet exist) on the page and when you hit the link you will be allowed to create the page "MP3".
You'll have to use the formatting system we chose though: WikiMedia. You can visit the Wiki User Guide to see how you format text.