I would recommend these videos.
Mixing and mastering are both huge subjects, and I don't think you'd find one video that
will cover everything. Learning how to mix and master takes a long time and a lot of
practise to get good results. Some people pick it up quicker than others.
this is just for fun then good for you, but don't expect to get good results straight
If you need professional results from the mix/master then hire a
professional mix/mastering engineer to do it for you. If you do take this route then
attend the session, because you can learn a lot just by watching a pro. You will learn a
lot more by doing this than watching a video.