To invite a friend, click the green "Invite a Friend" button in the top box of the Invitations & Referrals page.
You will need an email address to send the invitation. You have the option of filling out their first and last name. You can also have them automatically added to a campaign once they join by selecting one of your campaigns in the dropdown menu. Click the blue "Send Invitation" button to finish and send the form. Users that you invite this way are automatically added to your friends list. If your friend creates their own campaign at any point and subscribes to a paid tier, you will get a referral point.
When sending an invitation, you can also select a campaign. This will automatically add your friend to the selected campaign when they join using your invite. If you send an invitation that includes a campaign, and the user has not yet accepted the invitation, you can cancel the campaign invite by clicking the small red "X" icon. They will still be able to join Chronica, but will not be automatically added to the campaign.