I agree with jshortt. If I recall, he also recommended "Inside Pixinsight" to me when I was just starting out, and it truly is an excellent resource. But what I found MOST helpful for myself was following the step-by-step tutorials at the lightvortextastronomy link that he provides below. There's one in particular (
http://www.lightvortexastronomy.com/tutorial-pre-processing-calibrating-and-stacking-images-in-pixinsight.html) which I ALWAYS refer to when pre-processing my images. I've completed a couple of dozen images over the past year or so and am finding myself referring to the steps there less frequently, but it provided what I needed to be successful from the the very beginning--and success is what keeps you going.
Pixinsight can be very complex and intimidating, and I know I've barely scratch the surface. For example, I can now "deviate" from documented processes, but I still don't quite know what each function does and how it does it, so my deviations are all trial-and-error. My images are getting better, and it's also helped me improve my image-taking by seeing the results of various image-taking settings (changing apertures, image capture times, etc.).
Whatever approach you take, however, I would recommend sticking with ONE until you're comfortable with the interface of Pixinsight. You can find ten different ways to pro-process your images, and trying to follow each will confuse more than educate. So use one until you're comfortable before trying alternatives.
And good luck! It can be tough, but very rewarding!
