You can add a users to your invited event by following these steps:
Click the 'Add team member' button in the last row highlighted in blue. See figure below (Click on the image to enlarge it).
Type in the user's name and email address:Figure 2: Edit Event Team Membership
Click ‘Add to team’
The user has been added and appears in the 'Team' section.See figure below (Click on the image to enlarge it).