Add Users to your Meta / Facebook Business Account

Select your business account in the top left of the sidebar

Select 'People' underneath 'Users' in the sidebar

Click the 'Add' Button - this will popup an 'Invite People' Dialogue box

Enter the user's email address

Select Access Level - Employee Access or Admin Acccess

You may assign additional roles under "Advanced Settings"

This will typically be:

Pages: Content, Ads, Insights

Ad Accounts

Catalogues: Create Ads, Manage Catalogues

Pixels

Click "Invite" when ready