먹다 (eat) 먹이다 (help eat?!) 먹히다 (be eaten?!) 나는 밥을 먹다. (I eat rice) 나는 할머니에 의해 밥을 먹히다. (I'm eaten rice by grand mother?!) 할머니는 나를 먹이다. (Grand mother help me eat rice?!)

In your sentence, it would be "먹여 주다".^^/ ②I ⑤was fed ③lots of ④yummy stuff ① by my grandma. ① = (우리) 할머니는("my" in English is often translated as "우리" in Korean, not "나의" or "내") ② = 나에게(even though "I"is the subject) ③ = 많은 ④ = 맛있는 것을 ⑤ = 먹여 주셨다("먹여 주시다" is the honorific form of "먹여 주다") However if "lots of yammy stuff" in your sentence is omitted, it'd be "길러 주다". ②I ③was fed① by my grandma. ②I ③was fed ① by my grandma. ① = (우리) 할머니께서 ② = 나를 ③ = 길러 주셨다.("길러주시다" is the honorific form of "길러주다") \^o^/