In a nutshell, REST is going to help you speed up your development. If you are using a server side language like PHP and MySQL you are probably familiar with CRUD (Create, Read, Update, Delete). Manually writing this code can be laborious. If you could somehow use the URL to do this, you would then be entering the realm of REST. If you are using a framework like Ruby on Rails or Laravel, REST will be used a lot (and you will quickly see its power and efficiency).
Roy Fielding defined REST in his dissertation all the way back in 2010.
Wikipedia offers some useful information on REST.
And this video does a nice job explaining REST.