Moderator access must be requested though your Site Admin.
If you have adequate permissions, you can Invite Users at a lower permission level than yourself.
Another article in this section walks through the Share/Invite process.
Once you have Invited a User to a Workspace:
They will receive an email.
In that email is a link they will click which will bring them to the login of your Portal.
During their first login, they will enter their first and last name, and create a password.
The successful first login brings them directly into their assigned Workspace.

Any email notifications they receive moving forward on file or message activity will have a link that brings them immediately to the login (or resumes their session).
Or they can visit your website (if applicable) or visit your custom Portal URL to login to the Portal.