If you don't see the 'Add an Opening' button on the Openings page, it's likely that your account doesn't have permissions to create openings.
An admin user will need to enable the permissions for your account. You can have them go to User settings and select 'User Roles.' From here, they can click 'Actions' next to 'Regular User' and select 'Edit Role.' They'll want to mark the checkbox that says 'Create new positions and manage groups.'
This should allow you to create Openings!