Deciding which software to use is a blend of understanding what you’re trying to do and also choosing which software feels the most natural for you to use. For example I use Inkscape for almost everything, But some people just don’t like the interface of that program. There is an element of personal preference in that decision.
Here’s a link discussing various software options:
Once you’ve made a choice about which software you want to use or at least narrow it down, then you can start looking for webpages or videos that are about that software. As I said before there are so many resources out there, the first to decide what you want to know and then it’s just a matter of finding the person that’s taken the time to write it up or make videos about it.