Sorry for the newbie question but I can’t seem to figure out how to earn players without buying packs like last year. It says I need to acquire certain players from packs to play certain events... I’m lost and any basic guidance would be greatly appreciated

Ive been playing since MM16 yet I still can’t figure out a way to get better players without spending money. I’ve been playing the events but still have no idea where to go. The lack of sets confuses me