Before each race, you must activate a squad of four starting drivers on your team Roster page. This active group must include one driver from the A List, two from the B List, and one from the C List. The rest of your team members are reserves, who don't score fantasy points (except for qualifying bonus points).
To activate a driver, click the checkbox next to his name and then click "Save Selections."
The deadline to change the status of a driver on your team from reserve to active is five minutes before the scheduled start of each race (view the complete schedule). If you don't make any changes, your active drivers remain the same as they were for the previous race.
These deadlines are based on the original race schedule and don't change even if there's a delay to the start or finish of a given race.