If you know, please explain and possibly give me an example
I'll try to explain it a bit:
If you have an executable file...
...and set the suid (set user id) bit: The file will NOT run with the permissions of the user who tries to run it but with the permissions of the user who owns this file
...and set the guid (set group id) bit: The same as suid but with groups
...and set the t bit (sticky bit): (deprecated) After termination of the process it will be kept within memory
ls -l /bin/bash gives you
-rwxr-xr-x 1 root root
If you run this command (start the bash) you will have the rights of your local user account. If the suid bit would be set and you start the bash you would have root rights becaue root is the owner of the file. (This is a method often used by rootkits and trojans) Setting the suid/guid can be very DANGEROUS so be careful if you need that ever.
Also, is it true that a certain folder can only have one group and one owner?
That's partially correct. However you can use ACLs to have a flexible rights managment (different groups/users with different rights). Try to search google "linux acl" or try "man getfacl" or "man setfacl" to find more about it. ACLs -however- are not supported on every filesystem !!