There are many types of collectors.
Those that might want their favourite mons or favourite era therof to have in a frame on the wall.
Those that might want to actually play the game. Mathematically speaking I find it a flawed game on so many fronts (far worse than something like magic, not quite as awful as yugioh), and that is before we consider historical stuff, power creep and whatever else. Some still enjoy it though.
If you want to do this get a computerised version of it and master that first. If it is still something you want then you can start in earnest.
Those that might want to do it as an investment, or indeed a video of opening them in some cases (which is an even more curious area as it leaves unopened packs being worth more than their contents likely are as a form of speculation).
Investment means quality and rarity is king and that is where people get into the discussions of things, buying the fancy boxes/storage and whatever else.
For play and to have some in a frame on your wall as a nerd thing is a different matter.
Investment... I can teach you the real world version, and I can at least give you a start on the own little arena version.
The real world feeds from the little arena, though it has a few others. Its own little arena is where we get down and dirty with quality/grading, and price lists (which to say the obvious are basically someone's idea of things, no real interest in the future of things or indeed necessarily what you will get in reality).
I should also note that grading is not "factory fresh" on down but worse -- you could have a pack still in the wrapper and transported from the factory by armed guard in "won't set off the bomb" levels of vibration sensitivity, kept in an air conditioned vault for however many years it has been now and opened by a surgical robot that normally spends it days stitching together blood vessels. If the slicing machine was a bit dull that day when they were made, or they went in a bit on the wonk then it is not going to be top grade (and as they are cheap cards made by a company that sees them as a money printer, which they were, then they were not exactly built to last or to exacting specifications).
So yeah rarity, desirability and condition.
Not all cards were made and distributed in the same manner. Some were special editions, some were only released for tournaments/films/competitions/possibly Club Nintendo, alternative versions of some exist, some had more popular characters, some were better for the game and thus more sought after then an to this day "I did not get and could not afford a shiny charizard when I was 9, want one now it is 25 years later and I have some money to burn on some nostalgia...".
People will then make lists of what trading platforms are asking and getting, and how to modify that for grade. That is usually the origin of price lists. or maybe They might also have separate lists for the top grades and those for just play. Older gen cards are usually pricier for the rarer ones there but there are exceptions.
Some better ones will also note what they were this time last year and what the popularity is. Sometimes this will also be modified if a card is deemed illegal for competition play (usually price down).
The big boy investor will then care what the prices will be in a few years so they can sell off then, and whether they will be worth anything. My antique vase is still going to be an antique in 50 years. 50 years from now... well baseball cards are still valuable but whether people will see it more as an amusing novelty like I treat random board/card games I buy from flea markets/car boot sales/yard sales from dead old people that have some nice art from the time on them.
Many of the people you might see as respected authorities on collecting that are within the community though will be less concerned with long term and think it is always going to be like now, or maybe just with more price.
50 years is 50 years though, 10 might be more interesting or maybe the bubble will keep growing for another 5 years and thus you want to sell then. Said investors that might not care about the cards also see a nice way to earn some money and thus you wonder when they might all try to cash out (see comic book collecting crash).
Seen as they are also not exactly making more of them then you also have those that would seek to fake them, though I am less familiar here with the common things done and tells than I am for other card games. If ever some good fakes appeared (or a corrupt expert valuer/grader got in on it) then that could also tank the market a bit, especially if the investors also pull out at that time.
It gets more fun than that. The total supply ever made is not exactly known and you never know when some kid (or now potentially nearly 40 something) that shoved it all in a box in the attic will go up there and find them, check prices and flood the market with some others, and you also don't know how many kids kept them in their pocket, took them to school, shuffled them and wore down the ink, messed up the corners and ultimately threw them away.
If you are then doing condition you will want something that preserves them. Being cheap ink on cardboard then physical damage, moisture, in some cases a lack of moisture in the air, mould, heat, cold, insects, UV light and the list goes on.
You then have three grades of protection
1) Your basic folder with them in. Not great. Can bend a bit if someone handles them roughly, can probably still get wet but will be way better than nothing or just rattling loose in a tin (though a tin might have other perks).
2) Little slip wallets, sometimes will seal, sometimes will not.
3) Hard plastic. Kind of hard to play the game with them. However the best of all of those for protecting against all of the things noted. Expensive to buy as well as injection moulded case is rather more pricey to make than heat welding a couple of layers of clear plastic sheet together and then sending it into a slicing machine (maybe also punching some holds and buying a ring binder).
Some hard plastic will be designed to stop it moving, though you want to be careful not to bend it if it is too small, some will be designed to hold them whilst in a little slip wallet.
