id: Display user and group id’s.
useradd, usermod, uderdel: Addition, modification and deletion of users.
groupadd, groupmod, groupdel: Addition, modification and deletion of groups.
chage: change user password expiry information.
sudo: run commands with super user permissions. 
# useradd testuser		    (It will add a normal user)
# passwd testuser		    (It will set password for that user. Same command can be used to change password as well)
# useradd –d /opt/testuser1 testuser1 (It will create user with mentioned home directory)
# useradd –M testuser2		(It will create user without home directory)
# useradd –u 1005 testuser3	(It will create user with uid 1005)
# useradd –g unix testuser4	(It will create with different GID)
# useradd –G windows, admin, unix testuser5	(It will create user with multiple groups)
# useradd –e 2022-06-31 testuser6	(It will create user with expiry date)
# chage –l testuser6		(You can verify details using this command)
# useradd –f 30 testuser7	(User’s password will expire after 30 days)
# useradd –c “Test user” testuser8	(It will add comment to user)
# useradd –s /bin/sh testuser9	      (It will add mentioned shell to user)
# userdel testuser9		    (It will delete your account)
# userdel –r testuser8		(It will delete user with its home directory as well)
# userdel –f testuser7		(It will delete user forcefully)
# usermod –c “Updated comment” testuser1	(It will update comment to user)
# usermod –G unix testuser2	(It will add user to unix group)
# usermod –a –G unix testuser1	(It will add testuser1 to supplementary and primary group as well)
# usermod –g windows testuser1	(It will change primary group to wheel)
# usermod –d /opt/testuser1 testuser1	(It will change home directory of user)
# usermod –s /sbin/nologin testuser1	(It will change user’s default shell)	
# usermod –e 2022-10-01 testuser1	(It will change account expiry of testuser1)
# usermod –l testuser2 testuser10	(It will change login name)
# usermod –L testuser10		(It will lock your account, You can check ! Sign in /etc/shadow file as well before encrypted password)
# usermod –U testuser10		(It will unlock your account)
# usermod –u 1010 testuser10	(It will change UID of user)
# groupadd testgroup	        (It will create a group named testgroup)
# groupadd –g 3000 testgroup1	(It will create a group with mentioned gid)
# groupmod –n testgroup1 testgroup2	(It will change group from 1 to 2)
# groupmod –g 4000 testgroup1	(It will change gid to 4000 for testgroup1)
# groupdel testgroup2	    (It will delete group)	
# chage –l testuser1		(It will give you account aging information)
# chage –M 45 testuser1		(It will expire user password after 45 days)
# chage –W 15 testuser1		(It will prompt for warning of password expiration before 15 days)
# chage –d YYYY-MM-DD testuser1	(It will change last password change date)
# chage –E YYYY-MM-DD testuser1	(It will set account expiry date)
# chage –m num_days testuser1	(It will set minimum days in password change)
# chage –M -1 testuser1		(It will set password to never expire)
# chage –E -1 testuser1		(It will set account expire to never)
# chage –d 0 testuser1		(it will force to change his password at first login)
# chage –I 7 testuser1		(It will force user to be locked in 7 days of no activity)