It's possible for your account to be in multiple sites. This may happen if you work for multiple organizations that offer different training. To switch between sites, go to the Select a Site dropdown and change your site.
You also have the ability to set a Default Site. Your Default Site is the site you're brought to when you first log in. To set it, click on the Set As Default button in the Select a Site box. This button will only appear if you're viewing a site that is not your Default Site.