If you're learning to design on the Web, one of the trickiest aspects you'll come across is how to physically control the positioning of page elements. The best technique is to use tables, but these work very differently from the layout tools used in packages such as QuarkXPress, PageMaker or Illustrator.
It's essential to know exactly how you want your design to look before you start work in Dreamweaver, and an accurate comp created in Photoshop or Fireworks is a fundamental prerequisite to good table design. Even then, there's a knack to creating table structures that accurately and reliably control the positioning of page elements. The important thing is not to use a single table for the whole design, but rather to use tables inside other tables - a technique called nested tables.