Hither is a fancy or old-fashioned way to say "here." Your grandmother might jokingly call everyone for dinner by saying, "Come hither! Soup's on!"
Language experts consider hither to be a "fossil word," one that is still regularly used within various idioms despite being otherwise obsolete. You may find it in the phrases "hither and thither" or "hither and yon," both of which mean "here and there," in the sense of a disorganized or confused movement back and forth. Hither shares a root with its modern relative here.