Supporters have the the lowest level of functionality and access. By default, new users will be classed as Supporters.
To get more involved supporters must agree to the volunteer agreement, at which point they will be automatically upgraded to a Contributor. You can edit the volunteer confidentiality agreement under Organisation Settings > Invite & Manage Users.
Once your new users have signed the volunteer confidentiality agreement, they will become Contributors. Contributors will make up the majority of your members. They are the foot soldiers of your movement.
You will have team leaders for each of your teams. They are responsible for the work of their teams. They have specific functionality and data privileges focused on their team.
Managers are responsible for the overall running of the campaign. They have broad functionality and data privileges focused on their team.
Owners have access to all functionality and data.