If you wan't to use departments, so basically companies that have there own settings but use on common company card.
You have to create a mother company and assign the company card to this company and add the departments as sub companies.
Select the sub company that you want to use as department and select the File (1.) -> Company settings (2.) or press the CTRL + O combination.
Select the company that you want to use as department (3.) and press the OK (4.) button.
In the company settings select the Download settings and check the "Use mother company's company card" checkbox.
Now this company will use t he company card from it's mother company.