How Do I create a Name Code for a Invoice or receivers Document

I'm a novice! I've developed a Purchase Orders database for my employer. In this database I've managed to create text whare the data type is specified as Number. Eg: the Products table (there is the PK[ProductID], and the FK SupplierID[Number], CompanyID(CustomerID)[Number]these two FK appear as text in the datasheet. I'm trying to create a Code for the names of Suppliers, Employees etc. that would appear on a receiving document etc. Can anyone advise me on how to do this. I have three days until my contract ends. I'm employed as a project team member in a Private welfare sector company helping marginalized peoples.
Thank You very much
Andrew Wong