but how do you buy players on the web app if you dont have the game or any coins?
They give you free packs and coins.
You use those coins to open MORE packs, or try to make a profit by buying and trading on the transfer market.
Opening packs are trash usually, but opening packs are worth it during early access because you make so much money off 80 - 85 rated players. 80 rated Ramires was going for 30k coins, 82 rated Luiz was going for 27k, 82 - 85 rated CAMS like Eriksen, Gotze, and Nasri 50k easy.
Some 85 and 86 rated players were selling for a lot of coins, like Reus, Hazard and Yaya Toure were going for a ridiculous amount of coins. So you can make a decent amount of coins during early access, but after a week or two players prices start drop really fast. 85 rated Hazard and 84 rated Neymar still sells for a lot, though.
But I make a crazy amount of coins of TOTW. I remember I made 2 million profit just off TOTW CDM Lahm. I would win him in auction for 500k and turned around & sold him for 850k. But the prices change so fast, that I remember his buy now price dropped all the way to 450k while I was still holding 3 I won for 600k each, so I lost 500k coins, so you gotta be careful.