Most on line tutorials are incomplete due to lack of time or simply because some stuff should have been learned before. A few times I noticed the deliberate ommission of a couple of steps. I assume the worst (not really wanting to share the full process, like a cook who does not give the ingredient that makes the difference between good and mmm-good).
Everytime you see a tutorial about modifying pixels you see the experts at work doing this and that and when you try it it... well it does not work so well. This is normal, you are learning. The tutor should always suggest that you use his solution (and your exprimentation) on a seperate pixel layer making it easier for you to try again and again until you get it right.
Since you may not always be on line, download the tutorial using a browser plug in. That way you can have a small window open to follow through any time anywhere.
Use pause and rewind. Some folks give all the steps but they are so fast they are hard to catch. Having the video downloaded prevents a potential wait to go back.
When you look for a solution to a problem do not limit yourself to a few videos but consult dedicated web sites and forums. More often than not a solution exists but it is not widely shared. Astrophotography has a lot to offer and so does underwater photography. Why these two? Because they present problems that are consistant and rarely seen in 'normal' photography. I have learned more from these two post processing fields than any other.