Before guests can RSVP you will need to check and/or create you have the correct Guest List Groups for your needs. This will allow you to create groups of events that different guests groups are invited to (E.G - wedding ceremony & reception, Evening reception only) which will allow the system to know what your guests are RSVPing to and not show them details of any other events when they RSVP. You can see more about Guest List Groups here -

Free Simple RSVPs

If you have a free account you will need to add the 'contact us / RSVP' section to your website for guests to let you know if they can make it. If you upgrade to our GM+ membership there are multiple options to suit your needs. You can find more information about the RSVP options here -

RSVP using an email Address and sending email invitations

Storing an email address for the lead guest in each part will allow the system to identify the guests specifically and collect their response to the events they are assigned to. Once the guest has submitted and confirmed their RSVP your guestlist will automatically update with their response. Having an email address stored for your lead guest will also allow you to send email stationery to each guest party.

Guest List Group Passwords

Guest List Group passwords can be shared with the guests for each group which will allow the system to identify which events the guest is invited to and ask them to RSVP specifically to those only. 
You will then just need to accept the RSVP response via the blue request bar that will appear at the top of your guestlist and link it up to the correct guest name on your list or add them as a new guest to the list.
Once you have saved the guests details to your guestlist there is an option to send them a email link that will give them access to their personalised Guest Area Dashboard.

All guests are invited to all events - Open Access

If all guests are invited to all your events you can make the 'All Events' Guest list group 'Open Access' so guests won't need a password or email address to RSVP to all the events but you will still need to accept their RSVP onto your guestlist as you would with a Guest List Group password

Unique RSVP codes

You can enable the Unique RSVP codes in the RSVP settings page on your dashboard which would generate a code for each guest party. When a guest comes to RSVP and enters this code into the password box the system would identify exactly who they are (as it does with an email address) and automatically update the guest list with their response.

Unique code is just a term we use for couples so we can differentiate between Guest List Group passwords and individual guest party codes but the guests never see this term. Therefore you could call it a password on your invitations to save confusion when guests come to RSVP.