Your client's portal is where they see their posts and approve them. Nobody can sign in to it until you invite them.
- Open the client's page. On Clients, press their name.
- Press the Settings tab, then Access.
- Under Invite someone, type their email address and press Invite.
The page says Invitation sent. They get an email to set a password, then land on their portal.
Who has access lists everyone who can sign in to this client's portal. To see everyone across all your clients, press Everyone with portal access.