You would define two tables, one for Companies and one for contacts linked to those companies. there are then multiple options for seeing all the contacts associated with a given company, though a portal to contacts would be one of the simplest options to use.
Companies::__pkCompanyID = Contacts::_fkCompanyID
For an explanation of the notation that I am using, see the first post of: Common Forum Relationship and Field Notations Explained
Thank you. This was helpful.