The header section of the document serves several purposes. First, it contains the title of the document, which the computer automatically displays at the top of the browser. Additionally, the header section is used to define what are called meta tags. Meta tags are tags that describe the document that search engines use when they index Web pages. Not all search engines read these tags, but enough of them do that it is wise to include them in your pages. In addition, the header section is where programmers place any JavaScript code that is being used.
The BODY tag is used to enclose the content of the page. It is a required tag that has parameters that can be specified to control the look of some of the aspects of the page.
When you first start writing HTML code you may assume that when you end a sentence and go to a new line that your HTML output will also do the same. Not so. In HTML, whitespace is ignored, and without placing a tag at the end of the line it is assumed that you want to continue from where you left off.
The header tags are a quick way to change the size of your text. There are three levels of headings that are normally used, h1, h2, and h3. H1 is the largest and the others become increasingly smaller.