Answer:
Before you program in javascript you must learn HTML and know how to use it without Dream-weaver or any other similar programs. But lets say you have this prerequisite.
You now have two options you can either embed the Javascript anywhere in your HTML or in a separate js file.
To embed all you do is use the <script> tags
example: <script type="text/javascript">JAVASCRIPT HERE</script>
To put your javascript in a separate file you call it like this
example: <script type="text/javascript" src="THE URL OF YOU JAVASCRIPT CODE" />
This is how you open up Javascript
If you want to program it though you have to learn the language
Here are some examples
<script type="text/javascript">
document.writeln("Hello World");
</script>
The above code will write "Hello World" in a browser when ran.
<script type="text/javascript">
alert("Hello World");
</script>
The above code will make an error box or better called alert box, appear and it will say "Hello World"