Under Persons > employees new employees can be created.
Enter the first and last names and/or company name and at least the country under address.
Under "Type of customer" select "Employees". You can already assign a default sales office here to the employee.
Under "Authorisation" you can create a username and a password, you also grant the according rights, e.g. management, accounting, or administrator.
If you click on "Apply" the record will be saved.
To control the access rights more precisely, you can do this under the tab "Extended authorisation".