The first and most important part of managing users process is creating new users. To do this go to Setup > Administer > Manage Users > Users. Then click New User.
Then you’ll need to fill out details for the user: it’s fairly obvious stuff until you get to the role/profile/user license part which requires a bit more understanding.
Profile is a set of permissions which determines what users are allowed to read, write, edit and delete etc. User licenses determine what Salesforce features assignees are allowed to use. Roles define where they fit in the role hierarchy (which controls how access to data rolls up).
Once the user record has been created the person will receive a confirmation email at the address that was specified. To edit the user information, go to the user record and click edit.
Another important aspect of managing users is resetting passwords. To do this simply go to the user record and press Reset Password, which will reset their password and send them instructions via email. This can also be done en masse by clicking Reset Password(s) in the list of users.
If you want to experience the Salesforce org from the perspective of a particular user then go to their user record and click Login. This will “log you in” as that user so you can see first hand if they have access to something for example.
You can “Freeze” a user which will temporarily suspend their ability to access Salesforce. Finally, a user record can’t be deleted but it can be deactivated by deselecting the Active checkbox.