Both Jen Simmons and Rachel Andrew have lots of good resources for understanding the new CSS layout techniques. This article of Rachel's is a year old, but will still give you a good understanding of the differences between the two: https://rachelandrew.co.uk/archives/2016/03/30/should-i-use-...
Jen's got lots of great links here: http://jensimmons.com/post/feb-27-2017/learn-css-grid, including thoughts about how we're going to be able to use all these new layout techniques in ways both new and old.
It's an exciting time to be designing on the web :->