The part of Photoshop I use most is Adobe Camera Raw. In fact, I don't even use it in Photoshop—I just use Lightroom.
Lightroom is a fantastic application for photo library management and organization, and it happens to have a very powerful raw converter (editor). While it may not be the best raw converter on the market—DxO Optics Pro definitely has better noise reduction, and I did like some of the editing features in Capture One Pro when I tried it—it strikes a good balance for me. I really like the digital asset management features and the workflow I have set up, as it lets me go through a large set of images and find the few I like best and want to work on.
I do most of my editing within Lightroom. That includes setting white balance, working with the tones (blacks, shadows, mid-tones, highlights, whites), controlling color, doing noise reduction and sharpening, etc. With the newer versions (CC / 6) I even merge images for panorama or HDR, something I had to do in Photoshop before Lightroom CC / 6 were released. For the vast majority of my photos, I don't even use Photoshop at all.
Lightroom's editing tools are fairly easy and straightforward. When I just started using it, all I did was fiddle around with the sliders to see what each slider does. I mostly learned how to use it myself, simply by experimenting, though I did watch some YouTube videos with tips and instructions as well. It isn't nearly as complicated as using Photoshop's different tools and options.
It's not that Photoshop doesn't have a place, though. I do use it, especially when I need to do some specific local adjustments, or manipulations that are hard or impossible to do in Lightroom (such as removing or moving an object). But I won't be surprised if what I use is hardly 1% of all that's available in Photoshop—it is a complex application, with a whole bunch of tools that I don't even know exist.