well one way to do it is to click "Forums" in the top tool bar, then scroll down until you see the part that sees "Mibba.com" then the first forum is the "help forum" right below it you'll see a Subforums that sees "Mibba Profiles" click it and then scroll down and click on "Share your layouts" their you can find all kinds of layouts made by mibba users. Once you've found one one you like just copy and paste the code.(wear to past your code lol) go to "my mibba" and click on "Layout / HTML" (or CSS depending on the code)under "Profile" then just past the code and click "Save Changes" and that's it!
if you need any more help with this or anything ells fell free to ask:)