GitHub allows you to choose among three roles for a person in an organization: owners, members, and billing managers. We will not deal with the latter; if you want more information on this, refer to https://help.github.com/articles/adding-a-billing-manager-to-your-organization/.
Owners have full access to the organization and are in the highest level of the permissions chain. As far as the organization is concerned, they can invite and remove people, create and remove teams, create and remove repositories, as well as manage the permission levels of all people and repositories. They can also edit the organization settings.
Being a member is usually the default role when a new person gets in the organization. The least a member can do is create a new team and add existing team members and repositories to it.
A member can also be promoted to "Team maintainer" for...