If email invitations or Save the Dates are sent there will be a magic link for your guests to access your guest area and be able to RSVP. This means they will not need a RSVP code as they will be authorised through the link on the email invitation. 
However, Guests can access your guest area from the link on your wedding website providing you have enabled the ability for them to RSVP without email invitations when adding them to the guestlist. Enabling this will mean you guests can login using either the email address you have registered for them or a unique RSVP code that has been created for them.

When adding guests to the guest list you will firstly enter the names of the party members. Once this is saved a new page will appear which will give you the option to add an email address for the lead guest and enable them to RSVP without an email invitation. By enabling this function each guest will be assigned a unique code that can be used to access the guest area as well the option to use their email address.

Unfortunately, one code cannot be used for all your guests as the login details guests used are used to identify which events they are invited to and collect the relevant information needed. 

If your guest doesn't have a code or a registered email address they can still use the login area to contact you and give their email address. You will then be able to add their details to your guest list to enable their access.

If you would prefer to have no identifiers for your guests you could use the 'contact form' on your website and ask guests to RSVP that way. However, this would mean that you would need to update your guest list manually with their responses.