You start by creating or joining a league using one of the many fantasy football apps, which is just a group of people. If you are the one creating the league, you can set how many players you want to allow in, and can invite people you want to join, like friends. You can also just have it set up to have random people join your league.
The standard positions are QB, WR, RB, TE, K, DEF, and you basically pick IRL players/teams from those position to be on your fantasy team. The specific scoring system is adjustable, but for a basic run down, you draft (pick) your players before the season start, either automatically (computer selects for you) or manually, and those players can score you point when they play a game if they perform well.
So if you selected RB Josh Jacobs who is currently playing for Green Bay, when he runs the ball and gains yardage, it scores you points if you have him on your active roster. If he scores a touchdown, it gives you more points. Lots of point rules for each position that are adjustable by the league owner, but thats just a quick general example.
You will play a different person from your league every week. You basically just field certain players you think will perform well each week based on that NFL players upcoming matchup and past performances, and your teams score is an accumulation of all your active players points combined versus all your currently weeks opponents points combined. If your points are higher, you win that week, if theres are higher, you lose.
Basically, its like guessing which players will do well each week. People like it because its kind of a competition to showcase whos knowledge about the sport is better, with a lot of luck sprinkled in for extra gambling fun. You do not have to bet real money to play, I never have, but some people like to. Thats what the pools normally are, you buy a spot into a league and the winner of the league wins the buy in pool of all the players as a cash reward.
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