You do a draft at the beginning of the season to distribute the players. There is a pool of leftover players that can be swapped onto your team at any point in time.
Each week you start people on your team. If you are starting them, they get points based on what they do. The more points, the better. You also have bench spots, which are just players that you control, but don't give you points. They are just backups.
Each week you are matched up against another person in the league. Whichever person gets the most points (which is just the sum of all the starting players on the person's team) wins the week. The winner of the league is the person who has the best record (in terms of wins/losses) at the end of the season.
Much of your team is set since the draft is done. But you can modify your team by swapping undrafted players at any time. You could also talk to another person in the league and do a trade, where you swap players on your team for players on their team. There isn't a real mechanism to do this like there would be in normal fantasy sports, but presumably you would just both drop and add the relevant players, while writing a note to other people to not be dicks and pick off the relevant players.
So week 1 isn't really done since you could modify your starting lineup until game time. As the season goes on you typically do a number of things. These include benching players who are cold, dropping players who are just bad, adding players who are hot, trying to play the right matchups, trading players (lots of strategies here, including trying to sell high, buy people before they reach their peak, buy low, etc).
