A User Role can be simply defined as “what a user can do" and each User Role is made up of a collection of Permissions. A Permission is an on/off switch that either grants, or restricts, a User’s ability to perform a given action.
Let’s assume you wanted to have a User Role called “Generalist” and you wanted users with that role to be able to Schedule Interviews but not Post Jobs. In that scenario you would turn the Schedule Interview Permission On and the Post Jobs permission off. Now, any User that you assign to the Generalist Role could schedule interviews but not post jobs.