Guests should be added as parties that will be named on the same invitation and will RSVP together.
From the dashboard go into the 'Guest and RSVP' tile. There you will find a the 'add guest' button. The first name entered will be the lead guest - if you want to add a partner or group members choose the 'Add a group member or +1' option. Once you have added all members of the party click to save guests and move on to the next guest/group. Alternatively there is an option to bulk upload all guests at the top of the page.
You can find more information about how the GuestList works here - https://gettingmarried.co.uk/guest-list-user-guide/