Build your lineup by using the plus sign to add players. On mobile, you need to choose the slot you are going to fill first and then then you will be taken to the player list.
You can see additional information about a player by clicking or tapping their name. This will bring up their player card.
Flex and SuperFlex slots are filled based on other positions.
Once you fill the available slots for a certain position, the Flex and SuperFlex slots will be utilized.
In this example, on desktop, an additional WR is added, filling one of the Flex slots. On mobile, a second QB is, which goes into the SuperFlex slot automatically.
Once you have filled all of the player position slots, and have remained within the salary cap, hit Submit, Confirm your lineup and you're in!