There are many videos available on YouTube that talk about different aspects of doing mosaic overlay crochet. Below are some I have found the helpful. Because people explain processes differently and learn in different ways, feel free to search YouTube or Google for the aspect you are working on or trying to learn. Honestly, that has been the most helpful for me, to see a couple different ways of doing things and decide what will work best for me.

#1 Beginners Guide to Mosaic Crochet – the Basics – https://www.youtube.com/watch?v=HTigdTvdTLQ&t=754s

Hate weaving in yarn ends? Crochet a simple Envelope Border – https://www.youtube.com/watch?v=_NdexE-5Ncg

Easy Reversible Mosaic Overlay Crochet Stitch – https://www.youtube.com/shorts/zzmfowPJ_4E

How to read mosaic overlay charts – graphs – https://www.youtube.com/watch?v=fxEOEqiheVM