See this page for more details about group management:
https://help.ubuntu.com/lts/serverguide/user-management.html

• Print groups for the current process:
  $ groups mtitek group1 group2
  
• You can print the groups of a specific users:
  $ groups mtitek mtitek1 mtitek : mtitek group1 group2 mtitek1 : mtitek1

Use the groupadd command to add a new group (man groupadd):
Usage: groupadd [options] GROUP Options: -f, --force exit successfully if the group already exists
Examples:

• Create a group named "newgroup".
  $ sudo groupadd newgroup $ cat /etc/group | grep newgroup newgroup:x:1005:

Examples:

• Delete the group "newgroup": $ sudo groupdel newgroup