add an address book to another sheet

Hi guys need your help. I have a spreadsheet that works out my travel mileage.
What im looking to do is add an address book, to which I can add future customers to, into the workbook so that for future mileage claiming all I need do is select the customer and the postcode / mileage will transfer into the original sheet. This will also create me a customer database.

I have included the mileage sheet for you to see

I have no idea how to make this work hence I need your help