this TFT thing needs a tutorial. I can't figure out what I'm supposed to do, how items are gained, what the blob does during fight, how xp effects the character, what item combinations make. I don't mind readign a bit of instruction. It seems like you are making a big assumption this will automatically make sense to new players.
I'll try to help you out, I've helped a lot of friends so far so hopefully I can assist you.
this TFT thing needs a tutorial.
Very true, but it's in BETA remember this game is incomplete.
I can't figure out what I'm supposed to do,
In short you are looking for 3 things Champion Synergies. Great positioning. A Carry to put your items on.
how items are gained,
Items are only gained in 2 ways. Minions (randomly) Carousel: by moving your little legend to pick up a champion.
what the blob does during fight,
Nothing it's your way to interact with other players with emotes etc. It's your avatar. The only thing it does gameplay-wise is pick up units in the carousel.
how xp effects the character,
So XP does 2 things, it allows you to place more units on the board and access higher cost units. The best way to level up in "on curve" which is to only purchase level ups when you are in increments of 4 XP and will reach the next level
what item combinations make.
Here's a cool data base to help you out. https://tftactics.gg/
I don't mind readign a bit of instruction.
Okay, take that web site and find a powerful carry and build a comp around it getting synergies etc. My go to is Shyvana (because I have an obsession problem). Shyvana can have the synergies of Wild/Shapshifter/Dragon.
How you can do it is look for WW and Nid early. Then you want to find Ahri and usually a filler wild like Rengar for the buff until you find Gnar. Once you have your core 4 wilds
you want to focus on your 2 dragons. 
It's typically best to save your items until these 2 are on the board.
Getting a golden spatula can turn Shyvana into a Sorc using Yummi getting you a 4th Synergy.
This in an incredible powerful comp. IT has issues like not being able to transition well if you can't find something or dealing with CC or a Kass on Shyvana, but when it's online O boy is it good.
I know this turned out to be a very popular strategy, but I actually came up with this before TFT was on the PBE. ######I'm proud of myself. You can just find a champion you like a lot and design a strategy around it. See what happens. This game has no META yet explore and figure something out!!
Universal tips. Unless you REALLY need a champion do not look for champions in the Carousel, look for items and combinations that will assist you.
Do not always try to hit level 3.
Level 2 are your front line and primary means of winning. Do not try to make everyone a Level 3 you WILL fail. In my comp I rarely try to make Ahri a level 3 as it becomes extremely difficult later in the game.
Take pairs early. Don't let early level 2 champions slip through your fingers because they don't fit your comp.
ALL abilities used that are not a basic attack are AP DAMAGE. Do not think that any champion is not AP or cannot use AP. ALL champions use mana except Kass, however transformers use it once.
Good luck boss.
Exactly. Why the fuck I should be asking everything in chat and hoping people can expain it to me. They didn't even create a proper error messages. I can't do something and I have no idea why, cuz it doesn't tell me anything. Bullshit game implementation.
There are like a bunch of videos on YouTube if you search for literally a second
Go out of your way to barely lose the first round set, picking items / champions first is way better then any gold you might lose early.
