: What's up with my body? The attached profile images are views of my body from a few angles. I've been living with this body for a while, but it wasn't until a couple of months ago I really started to question myself. "Why

TL;DR: 18 y/o male, 140lbs, 5'8", don't really work out, asocial,
stressed and depressed. I'm looking to gain insight on my body and
health advice.

Insights on dietary habits would be super useful here! What we consume is an incredibly important consideration when we start a wellness journey. Especially since you mentioned being stressed and depressed; what we eat truly matters to every aspect of our health, including our mental health!
Research has found that there is a link between what one eats and our risk of depression. This analysis from Psychiatry Research concluded that:

"A dietary pattern characterized by a high intakes of fruit,
vegetables, whole grain, fish, olive oil, low-fat dairy and
antioxidants and low intakes of animal foods was apparently associated
with a decreased risk of depression. A dietary pattern characterized
by a high consumption of red and/or processed meat, refined grains,
sweets, high-fat dairy products, butter, potatoes and high-fat gravy,
and low intakes of fruits and vegetables is associated with an
increased risk of depression."

In addition to the above, the discomfort you're feeling about your midsection/abdomen, may also be a nutritional component. Exercising regularly is a piece of losing belly fat, but eating a healthy diet packed with lean protein, vegetables, fruit and legumes are key lifestyle changes that contribute to thinner midsections.
Check out Healthline's article that identifies 6 Simple Ways to Lose Belly Fat, Based on Science
The TL;DR Consider your nutrition. Clean it up and focus on clean, whole, single-ingredient foods. Lean protein and healthy fats will help you fuel your exercise goals. Gains in the gym ultimately will not be attainable if your diet and your mindset are not aligned.

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Your question is very general, and will therefore only attract general answers, so this will be that.

Fixing posture

While you don't mention this yourself, C.Lange makes a good point about posture in the comments. To elaborate, it's clear from your second picture (shoulders from the side), that your shoulders are slumped forward and your neck has a sort of forward direction. This is called kyphosis. To compare:

This is very much something to look out for with regards to looking better, as straightening your back will to some degree flatten your stomach because your chest will come up and out. Then, instead of having your belly fat look like a pouch hanging over your waist, it will spread that fat out a bit into a thinner layer.

To actually reduce belly fat over all, there are other great answers on this site already, so I don't need to re-iterate. E.g: What exercises should I perform to reduce fat on a specific area of my body?

Thankfully, a proper workout regimen will go a long way towards helping you fix your posture. But it's definitely something to pay close attention to. My best tip here is to focus a lot on your posterior chain. That is to say your back, butt, and hamstrings. Note, I'm not advising that you ignore the rest, but a lot of guys have a tendency to focus a LOT on the chest, but the chest serves to pull your shoulders forward, so that would only serve to make the kyphosis worse. Again, I'm not saying "ignore chest", but as a rule of thumb, I like to advise two back exercises for every chest exercise you do.

Gaining muscle

Since your goals here are very cookie-cutter (gain muscle, visible abs), we don't need to go into detail. Get a tried-and-true workout program. Don't try to make your own. You're bound to create an imbalanced program that neglects key muscle groups.

Some popular programs include

Starting Strength 5x5
Wendler's 5/3/1
and more

Try a program, stick with it for 6-8 months, and if your progress stagnates, jump to another one. No program is meant to last forever. Variation is key.

Sprinting

Since this is one of your goals, the basics here are pretty simple. Sprinting is an explosive exercise. Training explosive exercises (like sprinting) makes you better at explosive exercises (like sprinting). Personally, I love uphill intervals. It doesn't take a lot of time, and it builds power in your legs. This will help you out with leg exercises in the gym too (like squats and deadlifts).

Pullups

This is great, because it aligns with the posture point from earlier. Pullups build back muscles, and back muscles contribute to good posture.

In cases like this where you have a particular exercise you want to get better at, consider doing it 3-5 times a week. You mention that you struggle with pullups, but here's what you do. For any set of pullups:

do as many regular pullups as you can
continue the set by doing assisted or negative reps

Assisted reps are things that support you going up, such as a rubber band.

Negative reps are where you jump/climb to the top position, and spend 10-20 seconds on a slow and controlled descent.

These methods employ the exact same muscles as the regular exercise, allowing you to keep hitting them despite not being able to do any more regular reps.

Coincidentally, this is my best tip for getting started even if you can't do any regular pullups yet.

4-5 sets of this method (warmup NOT included), 3-5 times a week should give you a kickstart on your pullup progress.

Timing

Note: When I say "work out 3-5 times a week" in any context, use common sense to guide you. If you start having perpetually sore muscles, or you get chronically tired and fatigued, reduce the amount of workouts you do. That goes for any workout program.

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