Rhipsalidopsis gaertneri, or more commonly known as the Easter Cactus, is an epiphytic cactus that produces masses of large scarlet flowers in spring (it is called the Easter Cactus as it flowers around Easter in the Northern Hemisphere). The Easter Cactus needs a period of a few weeks of short days/long nights and cool temperatures before it will bloom. If your plant is kept indoors, place it in a covered area outside for the winter. It will often bloom more than once if conditions are favourable, and you may see a flush of flowers again in summer or autumn.
Rhipsalidopsis gaertneri (which seems to be the currently accepted name), is also known as Hatiora gaertneri or Schlumbergera gaertneri.
Place your Easter Cactus in a position that receives filtered light. It does not tolerate full sun. Plant in an organic mix such as an orchid mix, or peat with bark pieces and perlite mixed in for drainage. Water moderately in spring through autumn. Let it dry out slightly between watering, but do not let it dry out completely. Water less in winter - keep it only barely moist.