Its Simple
Open Your Notepad
Write your HTML and Javascript Code and save as "yourfilename.html"
Open it in you browser and play with your javascript program
for example i have create a simple alert message for you
<html>
<Head>
<Title>
My Javascript
</Title>
<script>
function myJavascriptFunction() {
alert("Hello! Welcome to my Javascript Sample!");
}
</script>
</Head>
<body>
<h2>Simple Alert Message using HTML AND JAVASCRIPT.</h2>
<button onclick="myJavascriptFunction()">Click Me</button>
</body>
</html>
Copy the above code and paste it in your notepad , save as Html and open the program in your webbrowser.