We advise you to first create the contact in the Contacts module. Afterwards you can click on the arrow next to ‘Contact information’ and choose ‘Link to company’. Then you can link the contact to the desired company.
The same thing is possible when you start from the company you want to link contacts to. Yet, if you choose this way, Teamleader will only let you fill in the name and the function of the contact. The additional information needs to be filled in separately on the contact page itself. Therefore, we recommend to choose the first way described to link a contact to a company. But you're free to choose of course!