Let's say that you have two groups:

• Group A: Should see all of the lessons that you create.
• Group B: Should only see lessons about dogs.

You would create two sites:

• Site A
• Site B

You would create two (or more) manuals:

• Dogs manual
• Everything else manual(s)

In Site A (the one for people who need to see all lessons) you would place both manuals.

In Site B (the one for people who can only see lessons about dogs) you would add the Dogs manual as a reference.

Whenever you update the Dogs manual, the updates will be reflected in both sites.

After you have your sites and manuals set up then you will need to assign viewers to each site to grant them access to the site.