Let's find out how we can create users in Salesforce. Just navigate to Setup | Manage Users | Users.
The New User button will open a form, as shown in the following screenshot, to fill in some details. The fields in red are mandatory, and you won't be able to save the information unless and until you fill in these details.
Activating a user
Activating or deactivating a user in Salesforce is just a matter of ticking a checkbox on the user's record.
The Chatter Free or Chatter Plus license can be upgraded to the Standard full license, but it is not possible the other way round, that is, a full license can't be downgraded to a Chatter ...