You can add existing contacts from your contacts list to an an event to populate your guests list. Your contacts list is a global list all your contacts and they can be shared between different events.
From your Contacts Page or Guests list page, click on the "Add Contacts to Guests List" link on the right corner of the page.
Click on the checkboxes to add the contacts to the guests list of the event. The companions of the guests are added automatically to the event.
Once the contacts are added to the event, you can track their RSVP statuses and any gift you received.
Please note that if you uncheck an existing checkbox, you will remove the guest and their data (e.g. RSVP, food selection, gifts) from your guests list. Since there's no undo, Marrily will confirm you before proceeding with the removal.