It's important that we first separate the users under members in your organization into org. members and project members.
Org. members will always appear first, and you can see that someone is an org. member if they have either the Admin or Member role.
Project members are not a part of your organization, but are part of a project within your organization. They will not have any role under Organization Role.
Org. members
By clicking on the three buttons behind an org. members, you are given three options:
Add to projects
This option lets you add the user to all projects in your organization. You are also given the option to override the new role in any project where they are already a member.
Make owner of all projects
This option will also add the user to all projects in your organization, but will in addition make them the Project Owner of all projects. This will remove the Project Owner title from all current owners, as there can only be one project owner. You are also given the option to override the new role in any project where they are already a member.
Block in all projects
This option will block the user from all projects they are a part of in your organization. This will remove their access to any project in your organization.
Project members
By clicking on the three buttons behind a project member, you are given two options:
Add to organization
This option allows you to add the user to your organization. You are given an option of which role the user should have. You can read more about adding users to your organization here. Additionaly you can read more about Organzational roles here.
Block in all projects
This option will block the user from all projects they are a part of in your organization. This will remove their access to any project in your organization.