This is the step-by-step. For what it is and how it fits the bigger picture, read Tenants in the reference.
What this is
This explains who your account belongs to, and how one login can work across several organisations. It is worth reading once, because it shapes how access and invitations work everywhere else.
Your account is yours
Your Cloudby account belongs to you, the person, not to any organisation. You sign in with your username, which is usually your email address, and that same login is yours to keep.
One account, many organisations
With a single login you can belong to several organisations and move between them using the organisation switcher at the top of the workspace. You do not need a separate account for each.
You join by invitation
Joining an organisation is invitation only. Someone who manages that organisation sends you an invitation (an invite code or email), and you accept it. An organisation cannot simply add you without that.
You can create organisations too
With a registration invitation you can set up your own organisation, become its administrator, and invite other people into it.
Your role differs per organisation
What you can see and do is set per organisation. You might be an administrator in one, a manager in another, and a limited user in a third. Each organisation controls your access within it.
Leaving an organisation
An organisation can remove you from itself, which ends your access to that one organisation. It does not touch your account or your access to any other organisation. Your account stays yours.