Here are some good intros to CSS Grid and several layout concepts. You can ignore teh code part and just concentrate on the Grid demos and the explanation. Its a good way to understand the 1Fr concept.
There are 3 in this series - https://youtu.be/ZPtpzuRajzM
Also if you have more time, here is a video about how web design has changed and the concepts should be familiar to many RW users. Again you can ignore the code and concentrate on the layouts as it explains many important concepts.