To do so, use “Invite Guests” option available on Event’s cover photo under “Settings” option. You will then be redirected to the “Invite Guests” page from where you can use various services as mentioned below:
1) You can invite your friends from web accounts on Gmail, Linkedin, Twitter, etc.
2) You can enter your friends’ email addresses manually to send invitations.
3) You can invite your friends on this site.