There are some programs that are useful, some that are brilliant, and some that achieve legendary status as world-changers. Photoshop is without doubt among the latter, an honour that hardly any other programs can claim. Starting life as a image manipulator made by Industrial Light and Magic employees, it was picked up by Adobe in the late 80s who have developed and improved it ever since.
It's had a considerable impact in various industries, such as graphic design, fashion, media and photography. Some people hold it accountable for catalysing fashion's unrealistic portrayal of the female form, others for enabling the boom in CGI. One thing's certain: the world will never be the same.
Before Photoshop, digitally manipulating images cost roughly $300 per hour, for the hire of a professional digital editor working on a complex, high-end machine on dedicated programs. While in the beginning Photoshop was still the preserve of users who could afford the cost of the software (and those who could afford Macs, whose OS was an original requirement for it to run), there is no doubt that it opened up the secrets of digital manipulation to many more people, a trend that is continuing as powerful tech becomes cheaper and universally available.
If you have even a fleeting interest in any form of visual arts, knowledge of Photoshop will be a considerable feather in your cap. It is a surprisingly intuitive program, with incredible flexibility, which allows you to pick up basic skills with ease. Don't be fooled by its initial ease-of-use, though: it has a suite of incredibly complex higher functions which require serious learning and practice to master fully. With these, it is possible to create any two-dimensional image one can imagine, with photo-realistic detail.
The best way to begin learning is to find a copy and just mess around with it. For students, Photoshop can be picked up for a fraction of its retail price. Most work places now own a collective copy. As soon as you grasp the basics (layers, filters etc), you can build upon this knowledge by taking courses or receiving tuition.
For would-be Photoshoppers, the latter option is a solid choice, because it enables you to learn at your own pace and fully grasp concepts, something that isn't always possible with classroom learning. You will also get far more time in the program than if you learnt with other people. Also, your tutor can tailor lessons to your end goal: the work-flow for mastering portraits is different than for creating digital paintings, for example.
Once you have a solid grasp of the program, learning other Adobe products we come easier. Premiere, Illustrator and AfterEffects all have degrees of commonality, for example. And, most importantly, endless visual potential will be at your fingertips.