There may be an event for which you’d really like to have someone attend. You have two choices: to invite them to that event or to enroll them.
Inviting to an event simply sends a notification to that person with a short message from you why you think this event is for them. It’s just an FYI and anyone can invite anyone.
To enroll a person to an event will sign them up as an attendee. Their seat will be allocated for them and they will start getting all the notifications related to that event. This requires a power user role, e.g. being an organizer.