Mixing is the process of combining and balancing all the individual tracks and elements of a song, including vocals, instruments, and effects, to create a cohesive and well-balanced stereo or multichannel audio mix.
Mastering is the final step in music production, where the stereo mix or individual tracks are processed to prepare them for distribution. It involves refining and optimizing the overall sound of a recording.
FabFilter: Beginner's Guide to EQ & Mixing and Mastering
FabFilter is one of the most famous audio processing companies, with their flagship product FabFilter Pro-Q 3 used by most professionals.
For beginners, the FabFilter YouTube Channel has everything you need to know to learn how to mix and master. Start with Beginner's Guide to EQ and supplement with Mixing and Mastering.
Mixing Masterclass with Bob Power
This video has gem upon gem. For more advanced mixers.
Guide for target frequencies with a glossary attached.