Offer plenty of opportunities. Give her lots of containers and, of course, stuff to put in them. Let her drop cereal bits into an empty yogurt carton or stuffed animals into a laundry basket.
Talk it up. Say "out" as you take a train out of the toy box and "in" as you put it back.
Enlist her help. During your next cleanup session, hand your baby a toy and ask her to drop it into a bin with the others. She'll be so pleased with her new skill, she'll want to help out over and over again (for now, anyway!).