Louis:

It may get a bit technical the following but if you play around you may get
somewhere.

To find the last row in the database use a function like this, where column
a contains data and there are on subtotals or other items below the last
record and DB is the name of the sheet:

Function getlastrow(ByVal sheetname As String) As Long
Dim a As Long
With Sheets(sheetname)
   a = .Cells(.Cells.Rows.Count, 1).End(xlUp).Row + 1
End With
getlastrow = a
End Function

To get the data from the form use a macro if it is a vba dialog form of if
it is a spreadsheet form use the following

' spreadsheet....
a= getlastrow("DB")
sheet("DB").cells( a,1) = sheet("form").range("B6")  ' say product id
sheet("DB").cells( a,2) = sheet("form").range("D6")  ' say quantity....
'.....repeat for each data entry in the form.

' form...
a= getlastrow("DB") ' get last row needs to be included in
                                  ' the form code or in the modules and
made public.
sheet("DB").cells( a, 1) = Me.TextBox1.Value
'.....repeat for each data entry in the form.

To get the items in the database use the match  function in a macro using

a = worksheetfunction.match(key, db,  0)  ' gives the offset from the start
of the db

therefore you use the cells function to add it to the db sheet.