Referencing cells based on a corresponding cell value

I have a wksheet that acts a template invoice with a corresponding auto increment invoice #. I'm having problems referencing the values of the # of rentals and their corresponding pick up and drop off dates. I need these values to go into the inventory out sheet from each invoice that is saved.

See attachment for further clarification.

I wasn't sure how to phrase the question, but if you look at the attached file you will see that there is an "invoice" with a save button which serves as a document to record all rentals from a rental program as well as the date of rental and the date of the reutrn of the rental.

Sorry i cannot write out all the code, the following one maybe can help you. you have to complete the code according to your company needs.

Workbooks("autosaveinvoice").Worksheets("Inventory Out").Activate
  Range("A4").Select
  If Range("A4").Value = "" Then
  Range("A4").Activate
  Else
  Range("A4").CurrentRegion.Select
  ActiveCell.Offset(Selection.Rows.Count, 0).Activate
  End If
  With ActiveCell
  .Value = Worksheets("invoice").Range("c3").Value
  .Offset(0, 1).Value = Worksheets("invoice").Range("c4").Value
  .Offset(0, 2).Value = Worksheets("invoice").Range("c6").Value
  End With