To Create a New User Profile -
Login to your wordpress AdminCP then go to Administration > Settings > General, users can create new profile themselves at http://www.yourblogurl.com/wp-register.php. Regardless of that setting, you can manually create new users here.
* Username (required) - Enter the username of the new user here. This will also be used as the Login name of the new user.
* First Name - Enter the first name of the new user here.
* Last Name - Enter the last name of the new user in this text box.
* E-mail (required) - Enter a valid e-mail address of the new user here.
* Website -: You may enter the new user's website URL in this text box.
* Password (twice) - Enter a password for the new user twice here, once in each text box.
* Role - Select the desired Role for this User from the drop-down box. (in your case you want him to write entries so select "AUTHOR".)
* Add User - Clicking this important button to save the new user's information into WordPress' database. If you don't click this button, the user will not be added. A flash message at the top of the panel well advise you that the new user has been added.