Permissions bits in Linux

SUID:
S instead of x in user permissions
It sets the process user owner to the file's user
It has no effect on directories
Set SUID:
chmod 4000 file
chmod u+s file

SGID:

S instaed of x in group permissions

It sets the process group owner to the file's group
Sets group for all new files in the directory, the same as directory's group
Set SGID:
chmod 2000 file
chmod g+s file

Sticky bit:
T instead of x in other permisiions
Files with sticky bit can be deleted onle by root ans files owner
Files in directory with sticky bit can be deleted only by root, file owner or directory owner, regardless of file permissions.
Set sticky bit:
chmod 1000 file
chmot o+t file