The information stored in a table when you select an item from a listbox
will be stored in the field defined as the listbox's Control Source. This
value comes from the listbox's Bound Column property. A single select
listbox has a value, a multiselect listbox doesn't. The value of the control
is a single item, not a set of items. That is why you're not seeing your
selections stored in the table field. A field should not hold a list of
items, it should only have one item stored in it.
To store your selected list of items, you need to store them in their own
table. This new table will have a field for the ID value of the record
you're on and a field for the value from the Bound Column of each item in
your selection list. It will actually be stored as several records, one for
each selection. You would then use a query to link the two tables together
on the ID field.
To do this with a listbox would require a bit of programming. Depending on
what you're trying to do, you may find a form/subform setup easier to use,
as this would store the "child" records in the second table automatically
for you.