You can feed it small chunks of meaty foods, like chopped up silversides, scallops, krill, etc. You should get a pair of wooden or plastic feeding tongs. Take a piece of food with the tongs and place it on the anemone's tentacles. It should move the food towards its mouth. Don't try to force feed it or stuff food in its mouth.
What kind of lights are you running? Are your parameters good? Anemones are hard to keep alive and require very high lighting and pristine water conditions. Good luck!