Ignore the pile on from some people @munnyya
If you were never taught how to cook, and you've managed sufficiently on your own, you don't know you're missing a skill until finances get in your way.
I'm glad you've had some good advice on here (ignoring the pearl clutchers).
Re dishwasher tablets, etc, Smol do free trials then a box of 30 tablets is £6.30. Otherwise I only buy what's on special offer at the supermarket and I look at the price per tablet thing on the shelf. If it's a decent brand for about 11-14p a tablet, I'll buy those! (Unless it's the lemon scented ones - can't stand them!)
In terms of food storage if you're batch cooking, I bought some plastic food containers from Amazon like you'd get from a takeaway (https://www.amazon.co.uk/10-Pack-Rectangular-Plastic-Containers-Leak-Proof/dp/B076T7651S/ref=sr_1_4?crid=3TDYVT4TMUHP6&dib=eyJ2IjoiMSJ9.MYE60IpeWF1dES4GqAzXbJVliV20239DW5T-w7iEStvAF9qXzmR_NoA4uJkqE7TYD9bJJI0hoHfp0SCw5Gf11TLHdDvJqXoGkyloEs83PhI3V85PGX3X0JQrpiw-TprsurwkqZTGS8c5XNA_ntWgNMhIxR_6VhUpWMJUnKzFVa3lGRAHciwkhQGJ5f9PnWa8BV8rK0_TLWAlPvRDh9K8bRBL_O2_ysQJ7TWP63mg06zQpZQ_jGOYEiurZbYn_QwO9Sbrb37owUfDdD9rEbMjvv439eTQPiKypfllS36SnmM.t4jTpCcxCWBNORH6ucpOoMPsRgG-lhu0IfU2nGdDG0Y&dib_tag=se&keywords=plastic+food+containers+with+lids&qid=1722938257&s=kitchen&sprefix=plastic+fod+%2Ckitchen%2C87&sr=1-4). They're reusable and clean nicely in the dishwasher. They're not the best quality for long term use, but they're cheap and I'm still using the ones I bought a year ago. Yes, nice glass dishes with lids are better, but they're also a lot more expensive and take up more room when empty.
Otherwise, if I make a lasagna, I put it in freezer bags.
BBC has a good article here about batch cooking, with links to recipes - https://www.bbcgoodfood.com/howto/guide/batch-cooking-beginners. Point 3 is the most important.
A tomato based pasta sauce can be used to hide a multitude of veggies and use up any veggies that are past their best, as can soups. My parents make a lot of soup and freeze it. They label everything but often have "surprise soup" lunches when the labelling's come off!
A roast chicken can go a long way too. Roast it on a Sunday then use it in pastas, salads, sandwiches for a few days after. You can pick up a small whole roast chicken for £3.22 in Tesco. They charge £4.50 for two pre-prepped chicken breasts.
You'd be worth buying some herbs and spice mixes that make even just plain chicken interesting. I like the Schwartz classic BBQ seasoning. It's £2 for a jar in tesco, but lasts a long time. https://www.tesco.com/groceries/en-GB/products/254777561 - goes well on chicken and on potato wedges. I make potato wedges and chips myself. As below, a baking potato is 23p at Tesco, which would also provide a portion of chips or wedges for 1. Just toss them in a bit of oil, sprinkle on some salt and pepper or anything else you fancy, and chuck in the oven on a baking tray for 35 mins (or an air fryer for about 25).
For a cheap meal you can't beat a jacket potato. One of my favourite meals when I lived alone was a couple of sausages chopped up and fried off, then served with a jacket potato piled with baked beans and some cheese (buy blocks, not pre-grated).
Jacket potato - £0.23 per potato
Sausages - £0.81 for 3 sausages from the tesco 12 pack that costs £3.25
Baked beans - £0.60 for a small tin of Branston (can't scrimp on beans IMO) or £0.80 for a big one out of a pack of 4
Grated cheese - £0.49 for 50g of a 550g pack of Cathedral City (again, I like CC cheese)
Total = £2.93 for dinner. If you bought 4 potatoes, the above would cost £12.77 and would give you four meals with half a pack of cheese left over. The sausages you can freeze (separate them first into portions as they can be a bugger if they stick together) and potatoes, cheese and beans last for ages if stored properly.
It's not the most nutritious of meals, granted, but it's a nice comfort meal.
I hope you take from this OP that it's ok to have not been taught these things and that I hope you feel a little excitement that you might be able to save some money but also create some lovely tasty meals for yourself.
I love watching cooking videos on tiktok and you tube!