You're not shit! That's why I ASKED if you'd had anyone teach you to cook properly. Most of it is easy but if nobody has shown you or allowed you to learn and develop your confidence in this that's not your fault. Changing family dynamics and cookery lessons at school being completely fucked for last 20-30 years has meant lots of people have fallen through the cracks on acquiring this skill.
I was lucky I grew up with a mum and 2 granny's who were fabulous cooks (one it was her job) who showed us (me and siblings/cousins) and let us make our mistakes without making a big deal of it - cook granny was a true whiz at rescuing curdled and lumpy mixes or excesses of ingredients.
I also had decent cookery lessons at school where we actually made 2 and 3 course meals from scratch and learnt the chemistry and physics involved and nutritional education.
Fizzy drinks - sparkling water is much healthier and cheaper and can be flavoured with a splash of squash or cordial or even fresh juices or fruits. I mainly drink this as I try to be caffeine free and also avoid certain artificial sweeteners. Sometimes I have it "plain" or I'll squirt a little lemon juice or lime juice in. Or you could get a soda stream, they're enjoying something of a revival at the moment and I bet the teens would have a blast with it!
Snacks - reduce consumption anyway. I'm a bugger for crisps but am also overweight and disabled so I try (I don't always succeed( to have carrot batons, celery sticks or sliced sweet peppers instead, for the savoury hit sprinkle with salt or even better garlic and herb salt grinder from B&M yum! You get your crunch and salty hit for much less calories and cheaper and more nutrients. Ok the salt not so healthy but...lesser of 2 evils. Chocolate - quality over quantity but you can still go own brand here, own brand dark choc is usually lush, or even better fruit, yes it's still sugary but still better than haribo etc
I think there's a food/recipe board on here you could post there for beginners recipes. I find BBC good food great for "basics" I use it when I've forgotten a recipes proportions or I know I've forgotten an ingredient and gone blank but also sometimes new recipes they're dead easy to follow and don't often include ingredients that are hard to get hold of.
But to kick you off:
Basic tomato pasta sauce: fry off onions and garlic then add either tinned chopped tomatoes or passata, basil, oregano and parsley simmer and serve - even better on the second day actually and in my experience stores fine in fridge for 2-3 days
Basic stir fry sauce - fry off garlic, ginger, chillis if you like, add dark soy sauce, splash of vinegar and again tinned toms or passata but not too wet or instead of tomatoes sweet chilli sauce. Add to stir fry and serve.
Cheats cheesey pasta sauce - fry off garlic and onions, reduce heat, add garlic & herb cream cheese, creme fraiche, grated cheddar stir until cheddar melted. Also lovely on jacket potatoes.
"I've recently turned 23" definitely forgive yourself - you are still very much learning.
How old is dh? I'm guessing at least 10 years older in which case he should know better than to be clinging on to a money guzzling car! Instead of putting pressure on you.