Hello Leidy,
Unfortunately, at this time, only a full Administrator can create new users. However, if you enable self registration, then you could allow users to create themselves (by registering for a new account). Or, if you connect your DSpace to a local LDAP or Shibboleth
(for authentication), then either system can be configured to auto-create new users (in DSpace) when they first login via LDAP or Shibboleth.
Obviously, once a new user account is created, it can be given permissions by different levels of administrators... for example Collection Admins can assign permissions within a Collection, and Community Admins can assign permissions within a Community.
Hopefully that helps, but let us know on this list if you have further questions.
Tim