Command to list SAMBA users

$ sudo pdbedit -L -v

-L to list users. -v to be verbose.

Add users who can access your shares with the ‘smbpasswd’ command.

$ sudo smbpasswd -a username
New SMB password:
Retype new SMB password:
Added user username.
$ sudo smbpasswd -e username
Enabled user username.

To change their password:

$ sudo  smbpasswd -a username
New SMB password:
Retype new SMB password:

Sources:

How to List SAMBA users
SAMBA : Server Guide
SAMBA : How to allow guest access