This is a nice way to get info about a user account :
# id korisnik1
uid=1034(user1) gid=1034(user1) groups=1034(group1)
This is very nice and useful especially if you have convolutet rights of acces on FTP servers.
If you want to add group to user (aside from the one given to him per default), it is done like this :
# usermod -a -G group2 user1
# id user1
uid=1034(user1) gid=1034(user1) groups=1034(group1),1326(group2)
How to see who are all the users inside one group :
# members mail
mail mail postfix user1 user2
Take care, this command is not per default in RHEL!