Relation (Lookup column)

Hi,

right now i'm stuck while trying to import my databases with existing relations.
I have a .XLS called Company and one called Contacts (relating to Accounts and Contacts).
In the Company file i have a line called CompanyID. In Contacts i have a line with CompanyID and one with ContactID.

How exactly can i import this relation between accounts and contacts so that i can see which contacts refer to company and the other way around? Do i need the lookup columns?

Thank you,
Lukas