First, let me tell you what Metal is; Metal is a set of tools which developers can use for 3D-rendering. It passes the OpenGL framework, which is slow and not very great for 3D graphics. So for simple terms, it makes rendering 3D graphics easier for your hardware and makes the performance of 3D rendering of the games and applications you’re using run better on your Mac. If you would like to learn more about Metal you can read more about Metal here.
While there may not be a ton of applications and games that have Metal support, but there are companies like Epic Games which are releasing games that have Metal integrated which will make 3D rendering for games even better. Games like f1 2016 and Warhammer 40,000 and apps like iMovie, Final Cut Pro X, Pixelmator all support Metal.
What Macs have support for Metal?
Quite a bit of Macs support Metal actually, just expect the Mac to be somewhat new. Below you can find a list of every Mac that has support for Metal.
MacBook (Early 2015)
MacBook Air (Mid 2012 or newer)
MacBook Pro (Mid 2012 or newer)
Mac mini (Late 2012 or newer)
iMac (Late 2012 or newer)
Mac Pro (Late 2013 or newer)
Just keep in mind that your Mac has to be updated to Mac OS X El Capitan (or later).