How do I read input data in a form?

I'm just starting to learn JavaScript and therefore do not know much about how Forms are used or how to read from them. I'm trying to play around with Google's Geocode, and need some help with building a JS Form to read from.

I have the following JS code, outputting the longitude & latitude, and simply need a form to store some addresses in. The code I have looks as follows:

var geocoder = new google.maps.Geocoder();
var address  = document.getElementById("address").value;
geocoder.geocode( {'address': address}, function(results, status) {
    if(status == google.maps.GeocoderStatus.OK)
    { 
        results[0].geometry.location.latitude
        results[0].geometry.location.longitude
    }
    else
    {
        alert("Geocode was not successful for the following reason: " + status)
    }
});

I'd like some help if possible to build a form this code can read an address from, where the ElementID = "address". How would such a form look? I'd much appreciate if someone could take a minute or two and explain how the JS works with the form. Any help is appreciated! Thank you, guys.

Solution

First create a Form in html. Include your external javascript file in it.

<head>
<script type="text/javascript" src="index.js"></script> //index.js is name of  javascript file which is in same location of this jsp page.
</head>
<body>
<form name="EmployeeDetails" action="ServletEmployee" method="post">
Employee Name:<input type="text" id="name"><br>
EmployeeID:<input type="text" id="employID"><br>
<input type="submit" value="Submit">
</form>  
<input type="button" name="Click" id="mybutton" onclick="myButtonClick">
</body>

In your external javascript file...that is index.js

window.onload = function(){ // function which reads the value from html form on load without any button click.
var employeename = document.getElementById("name").value;
var employeeid = document.getElementById("employID").value;
alert("Name : "+employeename+" : EmployeeID : "+employeeid);
}

function myButtonClick(){  // function to read value from html form on click of button.
var empname = document.getElementById("name").value;
var empid = document.getElementById("employID").value;
alert("Name : "+empname+" : EmployeeID : "+empid);
}