How to make simple form

[ZiNgA BuRgA]

Just search for a tutorial on the web - plenty out there.
HTML is pretty easy - it shouldn't take long to learn and is immensely helpful if you wish to do any form of customisation to your website.

After HTML, play around with the MyBB template system to get familiar with that - if you know HTML well, it should be easy to understand.
After that, follow the tutorial Sama34 posted above, making sure you understand each step - this should be enough to give you an idea of how to use XThreads.