It's been, well, a while since I routinely latched on to resources to help me get up to speed on photography, digital photography, and processing my photos...a lot of books, and then what was available online...
Of course there are the fundamentals, such as "Understanding Exposure", but I'll say that for the digital world, Scott Kelby books were a "favorite"!
As such, I have no hesitation in recommending his work to those getting started in digital photography and in the basics of the "digital darkroom", both in Lightroom and in Photoshop!