useradd (8) - Create a new user or update default new user information
adduser (8) - add a user or group to the system
passwd (1) - change user password
groupadd (8) - Create a new group
addgroup (8) - add a user or group to the system
Sinon sour Mdk il a userdrake pour ça.
(man nom_commande pour plus de détails)