"DHTML is the combination of several built-in browser features in fourth generation browsers that enable a web page to be more dynamic"

DHTML is NOT a scripting language (like JavaScript), but merely a browser feature- or enhancement- that gives your browser the ability to be dynamic. What you really want to learn is not DHTML itself, but rather, the syntax needed to use DHTML.

DHTML is a collection of features that together, enable your web page to be dynamic. I think its important now to define just what is meant by Dynamic?
"Dynamic" is defined as the ability of the browser to alter a web page's look and style after the document has loaded. I remember when I was learning JavaScript, I was taught that you could use the document.write() method of JavaScript to create webpages on the fly. For example:

<script>
document.write("This is text created on the fly!")
</script>

But what if we wanted to create content not only on the fly, but on demand? We can do that, by nesting the above code in a function, and calling it via a form button:

<input type="button" onClick="writeconent()" value="text">

Pressing the button will erase the entire web page and we were left with only the text the function produced.

That was back then. Now, with the introduction of DHTML, we can alter content on a web page on demand, whenever we feel like it, without having the browser erase everything else. That's what DHTML is all about. The ability of the browser to change look and style even after the document has loaded.

The technology of DHTML is currently at its development stage, with NE, IE 5 differing quite greatly in their implementation of this great technology. Its currently not possible to write one DHTML code and expect it to function in both browsers properly. Furthermore, the two browsers are at different stages in their development of DHTML; from my own knowledge and what I've heard, DHTML in IE is far more powerful and versatile than NS's.