The number of personalized email invitations and reminders that can be sent out each month varies per account:
Pro: 1000 per month
Ultra: 5000 per month
Enterprise: 50 000 per month
Additional emails can also be purchased as add-ons. For more information, please contact firstname.lastname@example.org.
Here is a video tutorial on email invites to get you started:
You can find more tutorials here.