The phrase before the verb keeps the item vague, meaning something like that, and 넣다 is putting it inside: a chicken cutlet into the dish, CG into a video, belts into a drawer organiser, flowers inside a pillow, a wedding photo into a frame, sweeteners into a drink. It is the everyday way of naming an example without committing to it. 넣다 is putting something in; 들어가다 is the thing going in by itself.