A command to list all users? And how to add, delete, modify users?

I need a command to list all users in terminal. And how to add, delete, modify users from terminal.

Solution:
 
To list all local users you can use:

cut -d: -f1 /etc/passwd
To list all users capable of authenticating (in some way), including non-local, see this reply: https://askubuntu.com/a/414561/571941

Some more useful user-management commands (also limited to local users):

To add a new user you can use:

sudo adduser new_username
or:

sudo useradd new_username
See also: What is the difference between adduser and useradd?

To remove/delete a user, first you can use:

sudo userdel username
Then you may want to delete the home directory for the deleted user account :

sudo rm -r /home/username
(Please use with caution the above command!)

To modify the username of a user:

usermod -l new_username old_username
To change the password for a user:

sudo passwd username
To change the shell for a user:

sudo chsh username
To change the details for a user (for example real name):

sudo chfn username
And, of course, see also: man adduser, man useradd, man userdel... and so on.