califdon is right. that's why I said in my earlier reply that the method you choose depends on the situation. If it's a small part of a title I want to align, I might use the positioning technique. If it's about multiple columns and boxes, you'd use floated divs.
If you really want to learn this I can recommend to study a book or two about CSS. Maybe "cascading style sheets" by brigs et al. It would really help to understand the basics first.