My sister has cuts on her arm and I need to know how to treat them quickly and without scarring. Some say to keep moist and covered?

Keep dry and clean. The treatment of any cut is to first rinde area clean under running water and dry it with clean gauze. If the cut is big and or bleeding alot, then take it to an urgent care /ER or your doctor for stiches. You may also need a tetanus booster.
keep it cleanly covered, and dry. change the dressing everyday.
Dr Ekole A.
Keep clean and soft. wash with clean tap water and soap, if not bleeding, let dry to air and when dry can apply vaseline or polysporin to prevent crusting. When exposed to germs keep covered, but otherwise keep opened to air.
Wound care. Wash area with water to remove particles.
Apply Triple Antibiotic cream or Polysporin Ointment from a pharmacy to prevent infection. Use a bandaid if cream might stain clothing.
Depending on clean or dirty wound might need a Tetanus Booster.
No way to prevent scarring it is part of new skin growth never the same as original. With good care can minimize skin damage. Get doctor advice for best care.