Log in to your Google Apps admin account from a web browser
From the Control Panel, select Organization & Users
Select "Create a new user"
Enter the new user's first & last name as well as the desired email address.
You can either make note of the temporary password or click "Set Password" (recommended) and then save.
Google will give you the option to email or print instructions for the user.
You can now select Done or Create another user
I recommend logging in as the user for the first time to accept the terms and conditions. To do this, simply logout of the control panel as the Google admin and then log in using the credentials of the newly created user. You will be have to confirm that you are human and accept the terms in order to finish creating the account. You can now log out as the new user and they can begin using their account.