The social networks in these days works as a powerful tool for the advertisment or say for promoting the store content.
Like Facebook as it has like button and share button which allow users to share it on web.

To add the Facebook "Like" button to your store follow these below steps:

1. Visit this link https://developers.facebook.com/docs/plugins/like-button,
and then on this link page in the bottom you will find a button "Get Code".

2. Click on the button as you will click a window will appear as show in screen shot below

change the href attribute with your url in the div at data-href.

3. Then open the view.phtml file in which past the 2nd step code of the screenshot at the line no 50 in view.phtml at the path /app/design/frontend/base/default/template/productalert/product/view.phtml 

<div class="fb-like" data-href="https://developers.facebook.com/docs/plugins/" data-layout="standard" data-action="like" data-show-faces="true" data-share="true"></div>

change the href attribute with your url in the div at data-href. 

4. Clear the chache of the setup from the Cache Storage Management section in system of admin panel.

5. Afterwards open the froontend of that setup and visit the product view page of any product you will find the like button there.