In order to add a user to a security role you need, when logged in as an administrator, to click the User Accounts button in the menu.
Click  beside the user will be added to the Security Role.
Click Manage Roles for this User at the bottom.

At Security Role, select the Security Role that the user will be added to.
If the role must have an expiration date, select a date from the calendar.
By checking “Send Notification” the user will be sent a notification email.
Click Add role and repeat the operation if you want to add the user to additional roles.
Click Cancel to return to the User Accounts page.