An editor helps you manage the wishlist, a guest just views it, and a reserver is a guest who has claimed a gift to give. Editors get invited by email. Guests only need the link.

Someone you invite by email to help run the wishlist. When you send the invite you pick the access level: Full Access, Contributor, or Viewer.

A Contributor adds wishes and can edit or remove the ones they added, but not wishes someone else added, and not the wishlist's name or settings. Full Access covers all of that plus renaming the list, changing its settings, and deleting it.

You grant this in your wishlist's access settings, and it has nothing to do with whether the wishlist is public or private. See "How do I invite another person to edit my wishlist?"

Anyone who opens your wishlist link. Viewer is also one of the levels you can grant by email invite.

A guest can view the wishlist and reserve items, if reservations are on. They can't add, edit, or delete wishes, and can't change settings. For an Anyone with the link or Public wishlist they need nothing but the link. See "Can people see my wishlist without an account?"

A guest who reserves a gift to signal they'll give it. The reservation locks the item so two people don't buy the same thing.

It isn't a purchase, though. Wishpicks takes no payment, and reserving doesn't fulfill the wish on its own. Reservers stay anonymous by default, and you won't even see that something was claimed unless you turn on Reveal reservations. See "How does gift reservation work?"

A guest and a reserver are the same person at two moments: viewing first, then claiming. An editor is a different role entirely, about running the list rather than giving from it.