1. add user to Linux system: 
    adduser user1
  2. add user to samba: 
    smbpasswd -a user1
  3. create group: 
    groupadd group1
  4. add user to group: 
    usermod -G group1 user1
  5. add user to different groups: 
    usermod -G group1,group2,group3 user1

change the ownership of the folder:

chgrp group1 /path/OfYourSharedFolder

give read/write access to your shared folder:

chmod 770 /path/OfYourSharedFolder