Galaxy Owners and Admins can add new people from their galaxy’s Manage screen. This is accessible via:

• The Manage button in the galaxy’s lobby
• The “Invite” button in the left sidebar

You can invite individual members via email from your galaxy’s Manage screen, and they’ll receive an invitation.

Inviting more people? Copy and share your galaxy’s Invite Link. Anyone with this link will be able to sign up directly to your galaxy.

See also: How do I change or delete my invite link?