Customizing 2010 theme

I am new to wordpress. I am trying to convert a regular html site I created to wordpress to take advantage of the extra features. My question is, where is the best place to insert html & css for each page. I know the page editor has the window for inserting some text or items etc. But, this does not seem to be the right way. Should I create a new page template for each page?

Thanks,
Mike