To create a new structure, use Structure | Create Structure menu or click Create Structure button on the Manage Structures page.
You need to specify at least the name of the new structure, and optionally description, permissions and other parameters. See Structure Details for description of the structure parameters.
When you create a new structure, you become the owner of the structure. Structure owner always has full access to the structure - see Structure Permissions.
Only logged in users who have access to the Structure Plugin are allowed to create new structures. See Who Has Access to the Structure.