I found this plant in a doctor's office. It was huge and beautiful. Happened to find two small plants like it on sale at a local store. Bought them, planted them but don't know what they are, maybe succulent or tropical. Please help me identify them.

A beautiful yellow leaf with almost a green leaf imprint in the middle. Stems on the larger plant in the doctor's office were nobby and reddish/brown. Gorgeous. Want to grow it successfully, but need to know its preferences, i.e. water, soil, location/exposure.