If your sign-in belongs to more than one company, a company switcher appears in the top bar beside the view switcher. It shows the name of the company you are in. Click it to open the Workspaces list; the app calls companies workspaces. The one marked Current is the one you are working in.
Under each company's name the list shows your access level in that company. All workspaces opens the full list on a page of its own.
Most people belong to one company and never see this. You will see it if, for example, you work for two firms that both use Terranix, or you are staff in one company and a client or consultant in another.
Not pictured: the company switcher appears only for a sign-in that belongs to more than one company, and the person in this guide belongs to one.