Organisations
An organisation is the standing team a project belongs to: a production company, a rental house, a freelance collective. Everyone in it reaches every project in it.
One account, many organisations. A freelancer who works for two companies has one FlexViz login and belongs to both. Accepting an invitation from a second organisation adds it to the same account.
Switching
The current organisation decides where a new project lands. If you belong to more than one, the header of your profile pages has a switcher at the top right; in the Explorer, the drive drop-down does the same. With only one organisation there is no switcher, because a list with one entry is noise.
Your choice is remembered on your account, not in the browser, so it is the same in every tab and on every computer.
Organisation settings
Administrators reach the organisation's pages from File › Profile…: the header there has Members and Organisation.
Organisation holds the name, logo, website, billing address and VAT ID, and the defaults a show starts from: units, time zone and language. A show's own rules still live with the project, in Project settings.
Recent activity on the same page lists who changed the organisation, its members, seats, projects and scene details, and when. Edits inside a scene are not there; they are in the scene's version history.
Your own time zone and language are on your profile and are the same in every organisation.
Guests have no organisation
Somebody you made a guest on one project, rather than a member, has no organisation of yours at all: no switcher, no organisation name. In their Explorer your project appears under Shared with you. That is the design, not a broken page. See Who can reach a project.