Some methods and tips for beginners that I learned while beginning to garden myself, and other discoveries. I am a beginner, don't rely too much on me.
Take a seed/growable part. Put it in the ground, deep enough so it is isolated but not so deep it can't grow. The ground can be store-bought (not too expensive and reusable), but you can just use the genuine ground you walk on in most places, depending on how fragile the vegetable is. Water it every day or every other day, depending on how humid it is. Watering every day is better though, you will notice when a plant has too much water, but when your plant gets visibly dry, it might already be too late. Plant it during spring/summer/autumn, and once the season has ended (3-6 months passed), collect the harvest.
Growing microgreens is nice but they are very fragile, it is actually quite difficult for a beginner to get it right. I have some experience now but still cannot get them to sprout properly.
If you are growing a plant, and it gets too large to support its own weight, tie it to a large stick you stick deep in the ground.
Leftover food remains don't have to be thrown in the trash - they can be used for composting - making a compost heap. Find some isolated container (because it stinks), of any size you want to get your compost to. I have one bigger than me in my garden, and it remains almost constantly full. Some of the things I throw in there: Rotten vegetables, meat, expired yogurts (basically rotten food in general), fruit/veg peels, eggshells. If you have weeds, don't throw those there, they might take over the whole compost.
Once the compost has sit there long enough, you can mix it with ground and use it for growing plants. The plants will extract the important nutrients out of the ground and their roots/branches will be able to grab onto the more solid parts of the compost.
Best way to make a compost heap is to leave a small opening at the bottom that can be closed/opened when needed. The best compost usually collects at the bottom after you have piled it up enough.
Some other things you can use to help your plants grow:
Growing your own potatoes is the easiest thing possible. Potatoes can survive winter, darkness, no water or air (though they do grow less in winter). A bag of potatoes once sprouted inside my drawer when i forgot it there for a few months. It actually yielded a couple small potatoes. Another time, I planted tomatoes, but after I did I realised I might have left a potato in the ground that I was planning to grill. I just left it there and a few months later, it yielded around 12.
If you got a sprouting potato left over, you will likely have it sprouting from both sides. This is great, you can cut it in half and get more growth out of it. Cut these potatoes as shown in image - smaller pieces are okay.
Leave them to dry. Plant them in a 1x1 meter container. It does not have to be fancy wood, I built mine out of leftover bricks and large rocks in my garden, it can be made out of anything as long as it doesn't rot in the rain and cold, even then it can be sustainable for one use.
Cover the potatoes with ground. If you did it right, after some time you will a little green pile of leaves pop out. Let those grow, and when they get too large, cover them with ground again. Do not cover the whole thing, let a decent chunk of green stick out!
If a green sliver starts to slide out your onion, you can grow it. These taste 10x better fresh than store-bought. Most people just put it in a glass of water, but I think a bit of ground works much better. What I did was I placed it in a random spot in my garden (on top of the grass already there), surrounded it by 3 bricks and a bit of ground. The green part has been growing for at least half a year now, I cut it every now and then for a snack, the difference between these when they are fresh and store-bought is amazing.
Peas grow surprisingly fast - about 2 months to harvest. Put them next to each other into holes at least 5cm apart. Deeper ground area is better.
Got nettles growing nearby? You can make a nice tea out of the leaves. Collect the leaves (USE GLOVES lol), wash them, let them dry until they get crunchy. Put them in a cup, pour in hot water. When they are dry like this, you can also put them in a sealed jar, and they last well for ages.
I recommend you mix it with other herbs, but even by itself, nettle tea has this very nice taste to it - it tastes exactly how you picture the taste of tea. No idea if it is good for you but it tastes nice :D You can also make soup out of the leaves, but every try I did tasted disgusting and inedible.
I once had a pothead recommend this to me and it works. Put a bunch of nettle leaves, stalks, whatever, into a jar. Fill the jar with water, close it, and leave it in the sun for about two weeks - it will get green/yellow. This acts as an amazing growth booster. Just pour a bit on the ground where you are growing your plants, along with usual water.
When you open the jar, it will literally smell like someone just took a poo. It has one of the most putrid, long-lasting smells I have ever experienced, do not use it if you want to spend the day on your garden/plantation, pouring a bit of this goop on the ground will it smell like a toilet for hours.
After about a month, its boosting effects weaken, the water will get brown, and it won't smell as much.