Like Rich said - it is the "800 pound gorilla". I have used it to create everything from simple website landing pages, online digital ads, photo retouching, enhancement and manipulation to magazine and newspaper editorial covers. It's very powerful and unless you are familiar with Adobe products, it can be very daunting to learn and master.
You can get a Creative Cloud license, where you have access to all of Adobe software for around $50.00 a month. A Photography plan is about $10 month, but you get access to Lightroom which gives you even more photo enhancement options. Definitely recommend the 'Dummies' book - it's a good reference once you start getting used to Photoshop. Adobe also has some quickie tutorials to get you started if you have something particular you need to do.
As long as the pictures are high enough resolution you can do most image editing. Lower resolution images are harder to work with, as the 'pixel' size is less, making it difficult to 'cut' images.
