When the user will click on image how to give him more information?

Answer 1

You can use JavaScript's onclick event.

Answer 2

You can use the title attribute inside the <a> tag or <img> tag and when you go over the image or link it will give show you more information.
Try:
<a href ="http://www.yourlinkhere.com" title="This is a link and you can write additional information about it inside the title attribute">your link</a>

<img src="yourimage.jpeg" title="This is an image of something and you can add any additional information about the image" />