Each Contact has a unique ContactID (Contact:ContactID - unique)
Each Company has a unique CompanyID (Company:CompanyID - unique)
Each Contact has a CompanyID (Contact:CompanyID)
You can put CompanyName field related by CompanyID from the Company Table on a Contact Record - it will show CompanyName.
You can put a Portal on the Company Record Layout that is related by Contact:CompanyID this will show Contacts with a Contacts:CompanyID that matches Company:CompanyID
You might find it useful to examine http://fmstartingpoint.com a free open template
Also the WhitePaper for FM Novices here http://www.foundationdbs.com/downloads.html