Please make sure to review our article on creating events. 

In certain cases, you may need to assign multiple staff members, or your client, to an event. Whoever is assigned to the event will receive the reminders, and if you assign your client, they'll be able to access the event through their client portal (if enabled). For more information on the client portal, please see this article.  

1) To assign multiple users or contacts to your event, scroll down to the user and contact fields at the bottom of the "New Event" window. You can assign as many users and contacts as necessary. 

Note: In order to be able to assign your clients (contacts) to the event, there needs to be an email address for them on file. 

If you assigned your client, they'll receive all the reminders you selected for this event, and will also be able to access the event through the client portal (if activated).