The body tag contains the code that generates what is seen in a browser.
This is what you see on your computer screen when you go to a web page, and most of the work you do is on code found between the opening and closing body tag.
In other words, now the fun begins – as does the aggravation, so I want to take a moment to help you get started right.
I have found that in general there are two kinds of web designers. Those with a background in computer science and those interested in design.
It's difficult to imagine two disciplines less alike, yet good web design takes some expertise in both. That will come in time – especially if you are careful to follow one simple, but crucial rule: Keep it simple!
That applies to both writing code and design. Indeed writing good clean simple code tends to result in good clean simple design* and vise versa.
Convoluted, messy code is difficult to debug and tweak – and even under the best of circumstances one spends a lot of time doing both.
There are a lot of wonderful things one can do on web pages. It's easy to get into the "wouldn't that be cool!" mode. I do it all the time – and yes, it might be very cool, but especially as a beginner it will probably drive you nuts getting it to work. That said, it's a gas when it finally does!
Remember, tags are containers. Sometimes they contain text, sometimes images. Often they contain more tags that in turn, contain text, images and more tags. (e.g. This sentence is inside five different tags.) Even doing everything you can to keep it simple, things can get complicated in a hurry.
* Here's a great site about what not to do: www.webpagesthatsuck.com.