How to grab a value from the database?

Hi... I stopped here in my program : I want to make a PHP page that reads from a mySQL Database.. This page displays two fields for the user : 1- Username. 2- Password. Now in the database there are many columns.. each one has many fields : Username, Password, Serial, Phone No., Address..Etc.. Now I want the PHP file to take the Username and Password after the user enter them in the fields and compare them with the ones inside the database.. if they are the same.. the serial field inside the database will send its value to the PHP page.. which will echo it as a variable ($var) there.. So every user has a column that has.. Waiting your replies.. Regards.. Hadi Aladdin