CSS Grid changes CSS layout in big ways, and it's browser support is quite good.
In order to fully understand CSS Grid, it's helpful to have both a meta-level view of where it fits into the CSS layout landscape, as well as a more narrow, micro-level view of how to write and implement the CSS itself.
Here is a list of resources to help you fully grok CSS Grid.
1. Where CSS fits into CSS layout history
In this video, Morten Rand-Hendriksen points out the shortcomings of past layout techniques, and how the simplicity of CSS Grid helps reduce HTML bloat and confusion.
2. CSS Tricks Guide
Chris Coyier of CSS Tricks breaks down techniques and terminology.
3. CSS Grid By Example
Rachel Andrew put together a great site full of different examples using CSS Grid. You can even alter the examples on CodePen.
4. CSS Grid Terminology
Lauralee Flores breaks down each CSS Grid term one by one with illustrated examples.
5. Learn CSS Grid
Finally, Jon Suh put together a site dedicated to helping you learn CSS Grid.
Have any other resources help you learn CSS grid? Be sure to leave them in the comments below.