[GirlySports]

Great explanations everyone.

I would only add this:

As you know teams that do well get promoted and teams they do poorly get relegated. Your immediate goal is to always win the league and gain promotion. There's also always a concurrent cup/knockout competition. The better you do, the more people see you, the more money the team makes and the more good players they can buy. Soccer is the ultimate free market sport.

Say you are a teenager (Around 16) playing for a high school team in Lethbridge.

Your goal would be to play for Lethbridge FC at a semi-professional level at like division 10 and hope some eyeballs see you and make a few dollars.

If a scout likes you then maybe a team like Red Deer FC will buy you and you end up in division 5.

Finally you're becoming a young star.. scouts are noticing you. Perhaps you get a spot on a Canadian Under-20 team etc etc...

Then the big break.. Calgary FC knocks on your door and they buy you. You're now in the Premiership.

And from there Calgary FC might qualify for other tournaments like UEfA Cup, Champions League etc etc.. whatever system is in place. All designed to make more money for you and your team. It's an extremely hirearchal system.

It's your job to play for your paid club. Playing for your country is extra.
However playing well in big tournaments can lead to a bigger contract. Again it's all about eyeballs seeing you play.