Inviting people to your event is a quick process, available on all Plans to all users. Here's a guide on how you can invite folks step-by-step.
Click on the Invite button for your event
Find the event you're looking to invite people to. Next, click the "Invite" button. You'll get a few options "Invite users" and "Invite channels". If you are looking to invite a specific person, choose "Invite users" and select the user from the list.
Some notes about inviting
You are only able to invite someone once. That person will receive their invite and no other invitations will be sent for the same event (this is to prevent duplicative invites).
Feel free to invite as many people as you like! If someone RSVPs to the event, it will be visible on the Details view of the event.