Adding Javascript file to WordPress, how to register script

Hello, I am trying to add a JavaScript file to my WordPress site. The file is called social.js and contains all the scripts for my facebook, twitter etc buttons, and some JS for a floating menu that appears on scroll on the post pages.

I have uploaded the file to my parent themes js folder, but am not sure where to go from here.

Do i use wp_register_script()

Do I use wp_enqueue_script()

Do i use something like this:

<script src="<?php echo get_template_directory_uri(); ?>/js/html5.js" type="text/javascript"></script>

Should I combine all these JS files into one?

I am using twenty twelve child theme.

Any advice would be greatly appreciated.

Thank you

James