Hi Sagar,
it is very basic concept.
you have screen element that map with a variable like wa_nonveg-chk_brnylike this so when you press order button it goes to PAI Event of screen so you create a work area of type of that table on which the data going to save.
then assign that work area field (For e.g wa_tbl)
so wa_tbl-chk_brny = wa_nonveg-chk_brny like this
then update the table by UPDATE COMMAND .