NET LOCALGROUP GRUPO_FTP /ADD
NET LOCALGROUP GRUPO_FTP usuario1 /ADD
NET LOCALGROUP GRUPO_FTP usuario2 /ADD
NET LOCALGROUP GRUPO_FTP

Fuente:

The NET command is used to manage user accounts and groups.

Syntax
      NET ACCOUNTS  [/FORCELOGOFF:{minutes | NO} ] [/MINPWLENGTH:length]
             [/MAXPWAGE:{days | UNLIMITED}] [/MINPWAGE:days] [/UNIQUEPW:number] [/DOMAIN]

      NET USER [username [password | *] [options]] [/DOMAIN]

      NET USER username {password | *} /ADD [options] [/DOMAIN]

      NET USER username [/DELETE] [/DOMAIN]

      NET USER username [/TIMES:{times | ALL]

      NET USER username [/ACTIVE: {YES | NO}]

      NET GROUP [groupname [/COMMENT:"text"]] [/DOMAIN]
      NET LOCALGROUP [groupname [/COMMENT:"text"]] [/DOMAIN]

      NET GROUP groupname {/ADD [/COMMENT:"text"] | /DELETE} [/DOMAIN]
      NET LOCALGROUP groupname {/ADD [/COMMENT:"text"] | /DELETE} [/DOMAIN]

      NET GROUP groupname username [...] {/ADD | /DELETE} [/DOMAIN]
      NET LOCALGROUP groupname username [...] {/ADD | /DELETE} [/DOMAIN]

View the current password & logon restrictions for the computer (plus machine role: Server/ Workstation).
NET ACCOUNTS

View the current password & logon restrictions for the domain.
NET ACCOUNTS /DOMAIN

Set the number of minutes a user has before being forced to log off when the account expires or valid logon hours expire
NET ACCOUNTS /FORCELOGOFF:minutes /DOMAIN

Prevent forced logoff when user accounts expire
NET ACCOUNTS /FORCELOGOFF:NO /DOMAIN

Set the minimum number of characters for a password.
NET ACCOUNTS /MINPWLEN:C /DOMAIN
The range is 0-14 characters; the default is 6 characters.

Set the maximum number of days that a password is valid.
NET ACCOUNTS /MAXPWAGE:dd /DOMAIN
The range is 1-49710; the default is 90 days.

Set passwords to never expire.
NET ACCOUNTS /MAXPWAGE:UNLIMITED /DOMAIN

Set a minimum number of days that must pass before a user can change a password (default = 0)
NET ACCOUNTS /MINPWAGE:dd /DOMAIN

Require that new passwords be different from ‘x’ number of previous passwords
NET ACCOUNTS /UNIQUEPW:x /DOMAIN
The range for ‘x’ is 1-24

Synchoronise the user accounts database (PDC and BDC)
NET ACCOUNTS /SYNC /DOMAIN

View user account details
NET USER [/DOMAIN]

Add a user account.
NET USER username {password | *} /ADD [options] [/DOMAIN]

Modify a user account.
NET USER [username [password | *] [options]] [/DOMAIN]

Delete a username
NET USER username [/DELETE] [/DOMAIN]

Generate a random password:
NET USER administrator /random

Add a group
NET GROUP groupname /ADD [/COMMENT:»text»] [/DOMAIN]
NET LOCALGROUP groupname /ADD [/COMMENT:»text»] [/DOMAIN]

Edit a group
NET GROUP [groupname [/COMMENT:»text»]] [/DOMAIN]
NET LOCALGROUP [groupname [/COMMENT:»text»]] [/DOMAIN]

Delete a group
NET GROUP groupname /DELETE [/DOMAIN]
NET LOCALGROUP groupname /DELETE [/DOMAIN]

Add a user to a group
NET GROUP groupname username […] /ADD [/DOMAIN]
NET LOCALGROUP groupname username […] /ADD [/DOMAIN]

Delete a user from a group
NET GROUP groupname username […] /DELETE [/DOMAIN]
NET LOCALGROUP groupname username […] /DELETE [/DOMAIN]

LOCALGROUP will create/modify a group that is local to the computer rather than an Active Directory domain-wide group.

Examples

Create a group

C:\> NET LOCALGROUP spud /add

Add to guests

C:\> NET LOCALGROUP guests spud /add

Then remove

C:\> NET LOCALGROUP guests spud /delete

C:\> NET LOCALGROUP spud /delete