Make a File Extension For a VB Project

I have VB express 2005. I am looking to create a file extension that I can use with my first VB project. I want it to save text like a .txt file but I want it to be a custom file extension like .bttf. I also need to know how to save the text in the text box to that file in my program. If this is possible I would love to know how.

Thanks