Create New Item In Table Based On Data In Controls When User Clicks On Button

I have a form free user feilds, some drop down which are populated by a database data and a button. I want to create a new line in a table when the user clicks on the button. the values for this new line will come from the Values (not visible content) of the drop box, the content of the text feild, the user ID that I should get from the connection and the current date... ie, I want do do a INSERT INTO table (userid, dropdown, text, date) values (how do I get the user ID from the session?, how do I get the value from the drop down?, how do I get the text from the text box?, how do I get the current date?)