2 great explainations of that: Check Martin Green at www.fontstuff.com and
Allen Browne at www.allenbrowne.com

You need code to extract the selected values from a multi-select list
box. You don't need code if the list box is not multi-select.

You can code the list box's Exit event....
Private Sub ListBoxName_Exit(Cancel As Integer)
' read the selected values

On Error GoTo Err_Handler
Dim strValue As String
Dim varItem As Variant
For Each varItem In Me.ListBoxName.ItemsSelected
strValue = strValue & Me.ListBoxName.ItemData(varItem) & ", "
Next varItem
strValue = Left(strValue, Len(strValue) - 2)
Me.ControlName = strValue

'Then clear the items from the list box
For Each varItem In Me.ListBoxName.ItemsSelected
   ListBoxName.Selected(varItem) = False
Next varItem

Exit_Sub:
   Exit Sub
Err_Handler:
   If Err = 5 Then
   Else
       MsgBox "Error #: " & Err.Number & " " & Err.Description
   End If
   Resume Exit_Sub

End Sub

this will display in a Form's control like this ....
Red, Blue, Green, Orange

However, STORING more than one value in a field is NOT a good idea.
The usual method of storing more than one value in a field for a
record is to use a sub-table bound to the main table by an ID field.
Then you can store as many values as you like as individual records in
the sub-table that are bound to a record in the main table.