When you sign up to Baresquare, a new organization is created; and you become the organization admin by default. This means you can change some settings (e.g., the organization name) and invite other admin users to your organization.
In case you have been granted access to more than one organization you can switch between them by heading to your user avatar in the top right corner and clicking on it.
The selected organization will appear at the top of the list (below the "Invite user" link), while all other organizations you can access, if any, will be listed at the bottom of the list (above the "Help" and "Logout" items).
Click on any of them to switch between the organizations you can access. You will be directed to the "Tickets" view in the selected organization, if tickets exist there. And you can follow the same actions for visiting another organization and its tickets, settings, etc.