Camilia, this is super easy to do with existing plugins, which you can find here: http://wordpress.org/extend/plugins/search.php?q=social+media
But if you’re keen to the coding yourself, and you have widgets in place, you could simply use the text widget that also allows for html and manually add your social media links something like:
<a href="http://twitter.com/YourUsername">Twitter</a><a href="http://facebook.com/YourPage">Facebook</a>
If you don’t have widgets in place, you simply need to access your templates footer in your directory. The path is usually something like: /wp-content/themes/yourtheme/footer.php