All you have to do is place two META tags named "description" and "keywords" in-between your <HEAD> and </HEAD> tags:
<HTML>
<HEAD>
<META NAME="description"
CONTENT="Come here to find
everything about blue marbles!">
<META NAME="keywords"
CONTENT="blue marbles,
marbles, marble information">
</HEAD>
<BODY>
<! rest of your page...>
</BODY>
</HTML>
The text colored in green of course should be changed to represent your page; don't forget to separate your keywords using commas.