It's not far at all from analog mediums. You can just use a basic round brush and start painting on top or underneath a line drawing- you can do and underpainting, like Justin Sweet might do, or you just jump right into it, like alot of speedpainters do. Becoming well versed with the tools is just a matter of experimentation- clicking every button, selecting every menu item. Even the 'Layers" panel has lots of secrets that many people are surprised to see when you show them; click a button, and then paint and see what changed. As long as you know the brush tool exists, you can work exactly like traditional paint: Big to small, "fat" over "lean", etc. There are also resources like Gnomon, or cheaper than that, youtube- where people have posted timelapse videos of their process. I think those might help you to actually see the process and get more cozy with it?
Best way to learn to paint in photoshop is to learn to paint from real life! Sitting out on the sidewalk or on a hiking trail with a canvas and some acrylics, or oil paints, and painting the light you see bouncing around- that's the fastest, easiest, and best way to get good at painting in photoshop, hands down. I think the majority of professional artists would tell you the same thing, too, ever since the invention of the paint tube in 1841. Look at Landscape painters: Monet, Sargent, Sorolla to name just three amazing painters... if you look around, you will find hundreds of miraculous artists who's work will help you learn.
haha, this is 3 years old nearly! This was around the time I started to learn about lighting in general: the way light acts on materials and form: How small amounts of bounce light where you wouldn't expect it could make a big difference, and how light and shadow can help push depth. Also probably just increased knowledge of color temperature.