Inserting a date format into sql using c#

Question

Hi, i'm really don't know programming but as i'm preparing for y graduation project i'm building a website. I want to insert a date format into my sql database. My date format is - month(dropdown list), date(textbox) and year(textbox). And i want to insert this date into my sql database whose datatype is datetime. plz tell me how can i insert this date format.