Flexbox is AMAZING! As you might imagine based on its name, it’s very flexible. In a nutshell, flexbox is a css layout framework for displaying and positioning parent elements and their children.
Flexbox can be a bit intimidating at first, but like most new things, the more you use it, the easier it gets.
The most challenging part of flexbox for me was getting the containers and flex items straight, but as soon as you do, it’s endless possibilities for your page layout and design. One of the very best resources I’ve found to reference flexbox, is css-tircks.com complete guide to Flexbox.
I’ve been using Flexbox more and more in my daily design and loving it.
Also, check out W3C Candidate Recommendation on CSS Flexible Box Layout Module Level 1