If you're talking about a sun coral, then put them in a low light area, on the bottom if your tank or under an over hang, since they're non-photosynthetic, they're naturally found in caves and low light areas. They need a good amount of flow and consistent feeding to keep the polyps out.
I'd recommend foods such as cyclopeeze, brine shrimp, and mysis for target feedings and smaller foods such as phytoplankton for indirect feeding
Good luck, sun corals aren't easy