Im sorry to say that the only anemone that doesnt need light tends to be the kinds you dont want in your tank (i.e. Aiptasia).
All normal "reef" anenomes need large amounts of light and absolute prestine water conditions. If the anenome doesnt have either of these then they simply "walk" or detach from rocks and go off in search of better conditions. As this is imposible in most home tanks this means the anenome is simply not going to settle down.
IMO No tank u nder 12 months of age should even contemplate trying an anemone as the tank will not be mature enough to sustain one.
Whilst Sabaes are easier anemones to keep this doesnt mean its easy... just less difficult than others.
Im afraid to say that the survial rates for anemone are devastatingly poor. For every 100 caught in the wild only 1 will make it to the wholesalers in any form of saleble condition.. for every 100 of these anemone that are supplied to the lfs only 1 will live longer than 6=12 months in home tanks. Shops sell them to the unwarey because people want them and thus they can be made money on. I have kept anemone and although they initially look relatively easy to care for, once you look into it deeper and realise that all sorts of considerations nd precautions have to be adhered to then you soon realise they are not anywhere near as easy as you first thought.
If the anemone is not attaching itself to the rocks or subrtate then this is a bad sign, turn off the powerheads for a few hours and see if this helps, failing this i would return the anemone quickly before it dies and polutes the tank.
As for feeding an anemone.. I dont.. if you feed them then they grow ... fast! i purtchased an atlantic anemone that was about 3inches acros. I fed this anemone every week with frozen cockly and within 6 months of owning it this anemone was over 1ft across!
Anemones will survive happily on the light (which is why the lights on the tank are so very i mportant) and what tiny floating bits of food it can collect in the water.
Sorry to be the vearer of bad news but I feel the shop has given very poor advise.