Hi jesicawillss, once you've regitered you need to 'add site' to your account. You can add multiple sites, as you need. You have to validate your sites, which either means adding a special <meta> tag to your html or if you already have Google Analytics added to your html you can validate it that way.
Once you have a site attached, Google will start to show you certain features of your website, like search terms where your site shows up on, main single keywords on your site, number of backlinks and where from and to, and many more features. I think it seems a bit basic at first, but once you understand more and delve into the rest of the features it really is helful.
I think the submit sitemap feature is very important. This tells Google what pages are on your site, so that it will make sure to index the ones you want, and of course, not the ones you dont want. I recommend making as much use of the 'help' section which will actually help a lot.