I use Darktable to do basic edits to RAW files from my Nikon D3100 and it's incredibly satisfying to understand and adjust exposure, lens correction, perspective, and a few other things. Darktable has module presets for many cameras, which helps. I still don't understand levels, color correction, and other more advanced modules, but there are many great videos on YouTube, and my final JPEGs often end up looking better than the camera's (I shoot in RAW+JPEG just in case).