hey guys do any one knows what kind of  engine oil should i use in my 4 valve car.  i went to buy engine oil but am found like 5W-30, 5W-40, 10W-20, 10W-30, 10W-40 and many more.  Do any one know what are those types for. and how much  quantity of oil should we use , as far as i know , 4 quart goes in 4 valve engine. 
anyone who have any good idea are appreciated to give some suggestion.