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:
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)