There are a few components that are needed in order to allow an external party to manage content on your site directly via the portal. This ensures they only have access to the areas you've given them permission to edit and not have access to the entire Control Panel. To get started, you need to ensure the following are in place:
Add the person to your CRM
Setup the company or location this person has access to, in the business directory (here)
Setup the element that you want to give them access to
Once these items are in place, you can go to the person or the directory to apply permissions. When applying it to the directory, this will ensure that all contacts to the directory profile have access. If you apply to the person/contact, only they will have this access.
To apply permissions to specific objects, you would need to go to the object itself (e.g. scheduler) and then assign the directory profile to the object. Look for a screen like this: