Note: I highly recommend creating a test blog. You can experiment with it before actually updating your own blog. Simply "create a blog" by using whatever name works. It will always be there for you to try new gadgets and design templates.
There are actually several ways to add tabs. In this video, I will show you how to add tabs by using the list gadget in Blogger.
If you have any questions, just let me know. I'm always happy to help.