As an actual artist I'm gonna give you an answer that's just gonna shortcut most of the guess work.
Everything you want to draw is made out of shapes, spheres, pyramids, boxes, cylinders etc.
Learning to draw is, quite simply, learning to break down the things you see into those shapes within your mind and then rebuilding it with those shapes on paper. For example, human torsos are often broken down into Boxes for men and more circular, curved shapes for women.
The easiest way to learn the shapes is to study the anatomy of the thing you want to draw. For organic, living things that's often learning stuff like muscle groups, shapes of the bones, planes of the body, body types and so on. Study each piece of it at a time, not all at once (arm studies one session, hand studies another session etc). This breaks information down for you and makes things easier to digest and, much better, easier to RETAIN. I'd suggest giving yourself as much time as you need to learn each part. If you need a month for arms, take a month. You need a year for hands? Take a year.
After you learn to do identify the shapes, you'll learn other principles like flow, shading, perspective, lighting and sources and so on. There are tools and exercises that exist to help with each one of these things, so you don't have to do it by yourself.
Next is find a community of other artists, preferably one with many artists who are professionally working OR (if none are available) just way better than you and seek their help and advice. I stress this one particularly. You can only do so much by yourself and having experienced artists point things out to you and give you tips and tricks will skyrocket your growth in amazing ways.
Also, reference, use it all the time because it's going to inform your decisions. I've never met an artist, professional or otherwise, who didn't use enough references to stuff an elephant like a thanksgiving turkey. Anyone who shames you for using reference or talks about how they don't need it or whatever, isn't worth listening to.
Finally, as has been pointed out by others, practice. You need to put in the time and the effort to not only learn this stuff but to go at it consistently. You will fail. Your drawings will come out hideous and they will make you feel bad, that is NORMAL. Every failure you see in your work tells your brain how to get better the next time you do it. Even if you don't notice it, you're growing because that's what learning is. The more you want to grow, the more this cycle will happen. And this is your warning, every artist I know is like this. As their skill grows higher and higher, they perceive ever smaller and smaller mistakes that most of us won't ever notice. This is the cost of art, not so much the time sink, but the psychological burden of wanting to eternally improve in it and knowing how, when and where to stop yourself. Da Vinci himself said art is never finished only abandoned because of this exact reason. Perfectionism creates great art but misarable artists, and you're going to need to learn that this WILL be one of your greatest fights.