The training section of Lunacore is divided in multiple sections, each showing different resources that can help you to increase your knowledge.
It's quite obvious that you need to learn how the basic tools in Photoshop work. Books, videos, internet tutorials, forums newsgroup or courses can help you with that.
Important to know is that to become an experienced Photoshop user you need to practice and experiment quite often. The other thing that's also important is that you find inspiration. Forums can be a source of inspiration (comments like "Nice job!" or when you notice that you're not the only one who's struggling with Photoshop) but also online galleries where you post your designs or art to find out how well you're improving after reading the comments of the viewers.
Important; don't throw away anything that you have made in Photoshop. It's especially your old designs that can inspire you, because they will show how well you have improved over time.
My motto has always been; "Don't look forward to see what you can't achieve, but look back to see what you have achieved!"
My personal suggestion for newcomers is; buy a video. Videos are fun to watch and not as boring to most people as a 300 pages book. A video can also give you a quick look on what Photoshop has to offer, so that you can make a decision in which areas you want to improve first. Don't focus in the beginning on things that are not important. If you don't use Photoshop for web design then don't invest time in slicing images for example, but focus on the most important things first.
A video is a good start, but it's always good to have a good reference book beside you. Check the books section for that.