When you 'optimize your lineup', the SquadQL optimizer will surface the highest projected lineup based on the players on your team.
You can also lock a player into your lineup if you want the highest projected lineup with specific players 'locked' in. In the example below, I locked in Isaiah Crowell into my lineup and want the best lineup with him involved:
Click on the lock button to make sure Crowell is in your optimized lineup
Lastly, you can add free agents from the Players or Player Research screen, and optimize a lineup with those [layers as starters. To do this, add players from those sections and go back to the Lineup screen. From there, you can optimize and upload to ESPN, CBS, or Yahoo.