The Rules of Engagement

Each Trial features one Little Sister and one Gather Corpse. The Gather lasts approximately 3:30 in duration.
Set the Little Sister down at the corpse to begin the Trial, then keep Splicers from interrupting her.
The ADAM multiplier will climb to a maximum of 4x as she gathers without interruption. The more ADAM you collect, the better your score and grade.
Only Thuggish, Leadhead, and Spider Splicers will try to interrupt the Little Sister. Big Daddies, Brute Splicers, and Houdini Splicers will only attack the player.
You only have access to a limited assortment of Plasmids, tonics, weapons, and ammunition types during each Trial.
You collect money automatically with each enemy killed. Spend this money at vending machines to collect more First-Aid Kits, EVE Hypos, and ammunition. The action will pause while you use the vending machine.
Pick up the Little Sister as soon as she stops gathering ADAM to end the Trial.
Complete the Trial to earn Stars. Each successive Trial within a location is worth one, two, or three Stars. Earn Stars to unlock concept art, video trailers, and additional Trials. See the Progress Menu for details.
There are six areas, each with three Trials and a Bonus Trial. Bonus Trials unlock after you complete all 18 other Trials.
You will receive an additional 40 ADAM upon completion of the Gather, just as in the main campaign.