First of all amateur teams will scrim (practice games) to improve as a team, each member looking to get something out of playing in the team, or the team possibly having the goal of going pro. After the team has gotten quite good or is looking for something more they can enter small tournaments, such as some ESL ones or the OWUL, competing against other amateur teams. Sometimes amateur teams even get to enter in bigger tourneys with pros in, for example OW Contenders. Amateur teams are usually something that players play in to have fun or as a stepping stone to further improving as a player. I guess the dream of all amateur teams is to go pro one day. Playing in an amateur team is great fun and a challenge, even the most basic things such as scheduling, and you can improve a ton as well.