Photoshop is a massive program, and has been the industry standard for editing photos since it first arrvied on the scene. I have been using it for 20 years, since version 4.0.
Although PS is a massive program and will do a million things for high-end professionals, you don't have to learn the entire program in order to start working on your photos and having some fun. In no time at all you'll find yourself staying up late at night doing all kinds of cool things to your photos. (Adobe also has a scaled-down, homeowner version of PS called Photoshop Elements. If you are just a hobbyist, that version might be more to your liking.)
If you are thinking about starting to learn Photoshop, thought I would tell you what Photoshop teachers have influenced me the most through the years.
NOTE: Photoshop is not a program you study for a while, learn it, and then use it the rest of your life. Learning everything about Photoshop can be a journey. I have been using PS for 20 years and to this day, still learn new things about the program. Plus, Adobe is constantly updating the program with new features, so you'll be learning new things every update.
FOR BEGINNER TO INTERMEDIATE USERS
Scott Kelby is probably the best known for getting a new user up and going with Photoshop. His lessons and books will help you get started and will give you some good basic knowledge of Photoshop. His tutorials can be humorous and fun to learn. He also will show you some easy to understand photo effects that will have you looking like an experienced Photoshop user in no time.
FOR INTERMEDIATE USERS
When you're ready to move into some serious Photoshop learning, Ben Willmore is the man. Not only will he show you how to do things in Photoshop, he goes 'behind-the-curtain' in Photoshop to show you whats going on when you work on your photos. Once you know and understand the concepts of what is happening when you edit your photos, you'll soon be tweaking and creating your own effects. He is easy to understand, often humourous, and not afraid to criticize Adobe when they've done something wrong. He has taught Photoshop to over 100,000 users on 6 different continents. I have read several of his books, and you will understand a lot about how Photoshop works when you read his books or watch his tutorials.
FOR ADVANCED USERS
When you're ready for some college type Photoshop instruction, I recommend MARTIN EVENING books. He is a well known fashion and portrait photographer based in London. His Photoshop For Photographers series are some of the best advanced learning books. His style of teaching is dry, and humourless, but guaranteed to make you an advanced Photoshop user when you've finished reading and studying his books. In my opinion, the best advanced Photoshop instruction out there.
Probably my favorite PS website is Photoshop Cafe, with Colin Smith. Lots of free, easy to learn tutorials, and this guy is really good. Been going to his site for almost the entire 20 years I've used Photoshop.
Another good instructor I've used is Julieanne Kost. She is an Adobe spokesperson and has some very good free tutorials.
These are the people who have helped me the most during my Photoshop career. Nowadays, you can find hundreds of tutorials on YouTube and other internet resources. While there may be some new, very good instructors out there, this article was meant to show you the ones that I learned from.
Although I do most of my mass photo management and editing now in Adobe Lightroom, I still use PS for special photo projects and professional portrait retouching.