How Do I: Restrict access

Beginner question, I have used Drupal in the past and am wanting to try out wordpress. I have a small business that has 4 departments, I want to restrict access to those departments to the users in those departments.

I installed the “groups” plugin thinking I could assign user to particular groups and then assign pages to be viewed by only members of that group. But this doesn’t seem to work this way.

what plugin do i need to install in order to restrict access to pages to specific groups of individuals?

Thanks