form input not updating tables

I have several forms to enter service records on
equipment. The main form(frmAddServiceDetails) has the
date, equip. #, and odometer as controls to add data and
several command buttons to open the appropriate subform
(form view, linked by the ServiceDetailsID). I can enter
data in the forms but it is not being input to the
underlying tables. I have an exit button on the subform
to close it and also one on the main form. I thought
records were saved when a form closed but if I go to the
tables there are no records. The forms are set up for
data entry and based on either the table or a query which
includes the table. Can someone tell me what I am missing?
Thanks for your help,
Walter