People above have told what a FAQ is. Now I'll tell you how to create one.
Click on the gear at the top of the page to get into Preferences. Click on your blog name on the left. Now in the Theme area click the Customize button.
In the left pane near the bottom of the list there'll be a Pages item, which reveals "Add". This is where you create a new page, which will have an address like yourblog.tumblr.com/faq -- so on this page you will write questions and answers about yourself, such as your name and location and what you ship.
So once you get some stuff onto that page, then you can create a link to it -- some theme sets will do this automatically, others don't so you have to add something to the HTML (editable on that same theme page) with a link to the FAQ page in the profile area.
Or instead of a page, you could just make a text post with information about you, catch the URL of the post, and put a link to it in your theme as mentioned above.