Flex Resource 1
Josh provides an in-depth tutorial explaining flexbox. It has a lot of examples and cover many of the proerties used to manipulate the flexbox module. He includes many visuals and interactive guides to help ease you into learning how to use this layout method.
Lear MoreFlex Resource 2
CSS Tricks website, which is always a great resource with lots of articles and tutorials, provides a "complete guide to flexbox". The explain how different flexbox properties work, share images of these properties in action and also make available a printable poster or "cheat sheet".
Flex Resource 3
Kevin Powell is a youtube creator who posts many videos about web development. I linked here just one of his many surrounding flexbox. He shows you how you can use the flexbox properties in your design. I highly recommend his channel, he covers many topics and is great with examples and explaining not only how properties work, but how to apply them to your work.
Summary
Flexbox starts to make designing layouts easier than trying to float things. You do not have to get as detailed with placement as it will work with you to make things flow and more responsive. It is a bit tricky to get used to at first, but gets easier and there is a lot of additional resources and guides out there to help you along the way.