Habits in Web application development [on hold]

I am going to develop php web application. (1) Are there any habits to perform form validation? (2) Are there any habits to do the update of the records list with checkbox checked? e.g. I have the list of items in the table list with checkbox per item, after checked some items and click save button, it will get the checked items for processing. In the web search, suggests to use session assignment variables. How to do?? Is there any sample code??