ES6 has a lot of new features. We are going to review those that we will use in the next chapters. If you are interested in learning more about what is new in ES6, I highly recommend you the book Understanding ECMAScript 6 by Nicholas C. Zakas which is available on Leanpub (https://leanpub.com/understandinges6/). There is also an online version of the book for free available at https://leanpub.com/understandinges6/read.
Also, there are other useful resources and tutorials like the one on Babel (https://babeljs.io/docs/learn-es2015/), an article on tutsplus (https://goo.gl/Qna5gl), a blog post (https://goo.gl/wme4jX) by Nicholas C. Zakas again, and a ton of stuff around the web!
Unsurprisingly, support varies wildly from engine to engine, with Mozilla tending to lead the way. ES6 compatibility table (https://kangax.github.io/compat-table/es6/) is a useful start for establishing what EC6 features your browser does and doesn't support.