[brundolf]

The OP is a good outline of the most important stuff. This is my favorite comprehensive introduction to flexbox: https://css-tricks.com/snippets/css/a-guide-to-flexbox/

And then follow it up with this one if you want to go a little deeper: https://css-tricks.com/flex-grow-is-weird/

Personally, I think flexbox is the single most versatile and important tool to be familiar with. You can create nearly any layout with it, in such a way that it's very naturally responsive almost by default.