Transfering data in Access

Hi,

I am having some problems in access, I have 2 tables with related forms.
1. company details
2. sales contract.
From company details form I have a command button which opens the sales contract form at a new record I have a field in company details called company number which has a unique number for each company, I would like to copy / transfer that value to the corresponding field in the sales contract form when it is opened by the command button, having that number in the field in sales contract pulls the address from the open record in company details form.

Help have been trying to do this for over a week now! New to access