There's going to be a lot of pictures here to make it easy getting started, so here we go:

1. Head To The Sites Page by click Sites on the menu bar.
2. Hit The New Site Button and fill the information properly to create the site:
3. Upon successful submission, you'll be brought back to the sites page, click the name of the site you just created in order to sign into that site.
4. When you see the big blue words at the top right hand corner change to the site name, it means you're logged into that site.

That's it! You're site is ready to be designed.