In the Calendar app, you can send meeting and event invitations. iCloud, Microsoft Exchange, and some CalDAV servers also let you send meeting invitations. (Not all calendar servers support every feature.)
Before you can invite people to events you’ve scheduled, you need to make sure your calendar accounts are turned on.
Go to Settings to select contacts.
Add an email address: Enter an email address, tap Return, then tap Done.
Note: In order to send a calendar invitation to a contact, the contact must have an email address. See on your iPad.
Tap an event that has attendees.
Tap Invitees, then tap Reply to invitations in Calendar on iPad