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, click on your profile image, and under the Select a Site dropdown 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.