This section is already partially treated within the permissions section.
By default user can exist without organization nor teams, however they would not be able to do any actions on anything, as every element is scoped within an organization.
To be able to create elements, then a user must first create an organization or be invited into one. Once an organization member, her/his permissions will be limited to what role have been assign to her/him.
Now that the user is within an organization a default role has been applied to her/him. But those permissions could be extended via the addition to teams.
Indeed teams can have multiple roles attached to it, and any members within those teams will have the same roles applied to them. Thus allowing extra actions.