Whenever I need to learn a new software, I just go to Youtube and pick a video that appeals to me most, or seems easy enough for me to start with. I think watching videos are the best way to learn Usually, those would suffice, especially if the software I'm trying to learn is related to one that I'm already familiar with, e.g. - in this case, Photoshop, Illustrator, etc. In my opinion, the best way to go about it is to learn some basic functions and buttons first, but just enough not to get too overwhelmed immediately. After that, then just find a nice existing design and just try to duplicate it as an exercise, and once you get used to it you'll be well on your way to making your own designs.

Cheers and good luck!