First critique

Hey, a couple of weeks ago I decided to seriously take up drawing, because before that I was afraid to admit my mediocre results to myself. Recently, I set a goal for myself in drawing, and now I realize that I need criticism in order to progress, no matter how emotionally taxing that might be. For the last week and a half, I've been practicing on this site with simple shapes and emotions. However, looking at the drawing, for now I only see one major, glaring flaw that I think really spoils the overall picture: the shadows. Even though I supposedly studied the theory, it seems that I practically don't understand the mechanism of how they work yet. I understand that shadows are far from the only problem, so I would like to hear opinions on all the aspects that I should work on, and how I can do that. I'd like to say don't judge harshly, but I understand that I need to develop, so I ask you to be honest.
https://imgur.com/a/40eaTnh

Hi Zoller!
Congrats on starting to seriously draw!! Its a really exciting time because you will see serious progress in only a few weeks/months! You are already good at proportions. The placement of everything is good! And yea, you did realize that shadows are the next big area to work on. Be bolder! Like, a lot bolder. Don't use HB pencils or lighter, use 3Bs or darker to loose the fear of going too dark. Dark shadows will really help create the depth and shape you are missing and looking for. 
If you can't figure out where to place the shadows you can try two things. First: stare at the picture/thing youre trying to replicate through super squinted eyes. This way you will see which parts stand out in darkness/lightness. Try drawing what you see with only two values (https://de.pinterest.com/pin/267330927876094049/) It will probably look weird at first but it really trains your eye! Think of shadows as dark fields and blocks of colour first. how to fade them out comes after. 
Second: Take some drawings that youve done already (like the one you showed here) and draw a 3d grid over it (like this: https://adventuresintheartofgames.wordpress.com/wp-content/uploads/2015/04/screenshot-2015-04-26-11-33-38.png) and think about where the lightsource is. The grid will help you better place the shadows because you can see the "hills and valleys" of the form. 

Good luck!! I believe in you! 
LG, Mikay