How to validate text box contents?

in my webiste (php , sql).. i have two text box for entering details and a submit button..
i need help in the code for validation of the contents in text box..

ie if i am clicking submit without entering details.. then it should display a message " enter details".. likewise for the other 2 textbox also..

code used to create the text box is given below..

<form action="index.{EXT}" method="POST"  enctype="multipart/form-data" onsubmit="return email_validate();">
	<table border="1" width="100%" bordercolor="#D0D0D0" bgcolor="">

    <tr>
	<td colspan="2" class="f-bold fs-11 bg-1 fc-FFF" align="center">Email Alerts</td>
	</tr>
	<tr>
	<td class="bg-EEE f-bold" width="200">Name</td>
	<td class="bg-F7F"><input type="text" id="name" name="name"  value="{rates.NAME}"  class="box-100" /></td>
	</tr>
	<tr>
	<td class="bg-EEE f-bold" width="200">Email</td>
	<td class="bg-F7F"><input type="text" id="email" name="email"  value="{rates.EMAIL}"  class="box-100" /></td>
	</tr>
	<tr>
     <td colspan="2" align="center"><input type="submit" name="submit" value=" Submit " class="button f-bold pb-3" />

    </td>
    </tr>
	</table>
	</form>

HTML:

pls help me....