Remarketing works especially well when combined with an active inbound campaign. By virtue of catching visitors to your website and remarketing and redirecting them to your inbound page/s you catch all the users to your site.
Which is a long way of saying, if you're going to do remarketing, don't just send them back to your site. They've already been there. Give them some extra value by sending them to a particular landing page or offer.
The best case is actually remarketing to those who didn't convert on your inbound landing page and remarket them to a different offer on your site. As they didn't convert but did visit they have shown interest in your product/service in some way.
As for what is is and how to do it, Goolge put together some basic vids on youtube. Check em out they're actually pretty well done for new and experienced users.
Google Videos -> https://youtu.be/_U8MmSa0KQw?list=PL...y6Vq7xDiQjlmwn