CSS-TRICKS

CSS-Tricks

The comprehensive guide provided by css-tricks explains grid layouts and its associated properties. It breaks down grid layouts based on property/value pairs for parents and their children.

MDN

Mozilla Developer Network

MDN provides a detailed description of the grid layout, and provides an in-browser css editor to test the impact of certain properties real time. Examples are provided for each property and value, and grid arrangement.

Learn CSS Grid

LEARN CSS GRID

This site provides a breakdown of the various grid related properties and values, and provides a visual example of the impact of each.

Special Mention: Kevin Powell's YouTube Channel

The EASIEST way to get started with CSS GRID

Kevin has a quick outline of the benefits of grid layouts, how they are used, and why they are used vs. flex.

Summary

There are a number of solid resources to learn how grid layouts work, similar to flex, and most of them work best to aid you while you are working on your own examples.