Start with the idea of using [X]HTML to mark up the meaning of your document, not the appearance. Then use CSS styling -- whether via external style sheets, style blocks in the HEAD section, and/or inline style attributes -- to control the appearance of the page.
To this end, the w3.org specifications for [X]HTML have now deprecated most elements and attributes which were used to control appearance in order to support the idea of using CSS for that.
If you browse the CSS forum here, you will find a number of good (and some perhaps not so good) links to learning sites and books. As you go through the learning process, keep referring to the relative parts of the specifications at w3.org (see below) so that you learn to read and interpret them. Once you become comfortable working with those spec.'s, which are the ultimate reference source (though not the most user-friendly), you'll be less dependent on others' interpretations of them.