Application Express :: How To Call Function Behind The Button And Update Only Specific Record

1 - i want to ask few things as i m new to apex, i am using apex 4.1, and created 3 select list and a button in selecting of parameter,

1 select list : select area
2 select list: select product
3- select list - size of the product

i want to generate Ids for the following. for that i created query for INSERTING RECORD FROM ONE TABLE TO ANOTHER , generation the ids when button pressed "Generate" after selecting parameters,

Now where i call that QUERY on button ? because when i create button its gives me option to submit, defined dynamic action, etc, where i call the function name id_generation when button pressed?

2- second thing i created tabular " select user_id, product_name, product_type from product".

By default check box list are create delete submit button are created, first when i insert record it saves that was fine, e.g i entered 50 records and afterward i want to update only one record, e.g there is a record product name = box, if i change it to box small and click submit then it saves all the page means all 50 records,

I want to submit only that record that i changed, for that i use the logic that only those records should be updated which are checked but the user. how will i do this ?