Drawing/painting books? How do I improve my drawing?

I like to draw/sketch/paint. I haven’t learned it in college; I draw just because I like. But, when I see drawings of those from fine/commercial arts, I think I’d need some training or tutorials. Do you know any good books on that that I can go through?
How do they make it so realistic?

Also, I’ve been told to study human anatomy. Any books for this?

Any suggestions are appreciated.