CSS Grid Layout Crash Course
https://www.youtube.com/watch?v=jV8B24rSN5o

Incredibly Easy Layouts with CSS Grid
https://www.youtube.com/watch?v=tFKrK4eAiUQ

 

Practice by playing
http://flexboxfroggy.com/
http://cssgridgarden.com/

 

CSS Reference
https://developer.mozilla.org/en-US/docs/Web/CSS/Reference

 

Learn CSS
https://www.w3schools.com/css/default.asp