Additional Resources

Power Query Documentation

For a good intro to Power Query basics (or sometimes when you just need a quick reference for some forgotten basics):
https://radacad.com/basics-of-m-power-query-formula-language

A good Microsoft starting point for Power Query resources: https://powerquery.microsoft.com/en-us/

From the above Microsoft site, you can find two really good references:

Power Query Documentation: https://docs.microsoft.com/en-us/power-query/
M Language Reference: https://docs.microsoft.com/en-us/powerquery-m/

Power Query Videos

Sometimes it is easier to learn by seeing and following along. The Learnit Training YouTube channel has produced 3 good videos to make you an expert in no time, complete with examples to use to follow along. Each video is roughly 2 hours, but allow for a couple hours per course to also do the examples and experiment along the way.

Beginner course: https://www.youtube.com/watch?v=i3CSD7bMMbg

Intermediate course: https://www.youtube.com/watch?v=ppD-jKqsqKM

Master course: https://www.youtube.com/watch?v=i3wZRgx_gpY

DAX Reference

A little outside Power Query, but often used hand in hand with the models in Power BI and Excel, DAX expressions are a powerful tool that is often referred to in the videos above. For those interested in learning a little more:

DAX Language Reference: https://docs.microsoft.com/en-us/dax/