When you learned to set read, write and execute bits on files and folders, you probably realized that you used all the available “spots” for permissions. So when manipulating special permissions, you sort of re-use existing permission bits. It functions just like any other permission attribute, but they’re represented a bit oddly.
Every section of the permissions string (user, group, other) has an additional “special” permission bit that can be set just like rwx. The indication for whether those bits are set is shown on the execute section of the string.