I just shared Layoutit grid site to my team last week. This site can take someone that doesn't understand grid to making a kick-ass layout in mere seconds. There's no other grid playground like it.
There is a similar site I recommend for people learning Flexbox here:
We open-sourced Layoutit Grid just a few weeks ago. There is still a lot of features we would like to add to showcase even more how powerful CSS Grid is. In case someone wants to help us out!
https://github.com/Leniolabs/layoutit-grid
I know it goes against the merits of the site, but it would be great if there was a fallback option to output CSS for browsers that do not support grids.
This would be pretty difficult, since at least some of the concepts of Grid (namely, anything involving calculation or auto-placement) are simply not supportable in old browsers.
There is a similar site I recommend for people learning Flexbox here:
https://codepen.io/justd/full/yydezN/
(That flexbox tutorial is hosted elsewhere too but the ads are less intrusive on the codepen site)