The next thing to do is go over to http://www.tumblr.com, and you will have a few details to insert. Your email address, a password and a url.

The url is going to be the text you are using in your backlink.

You also can't use forward slash ( / ) or other characters. You can use dashes though. So you can't use it for inner pages on your site. (deep linking). It'll go to home page.

so lets say you are trying to rank for the term "Cure For Hiccups" for whatever reason. That's the term you use for the url.

The url for that term will be cure-for-hiccups.tumblr.com

The site will automatically set the .tumblr.com as a subdomain. All you need will be cure-for-hiccups and you'll see it add the tumblr part to the end of the url automatically.