as you know plants use photosynthesis to create food for themselves and for other reasons. so basically photosynthesis happens in the leaves of a plant. Chloroplasts are in the leaves. photosynthesis happens in these chloroplasts which contain the green pigment, chlorophyll, thylakoids, stroma, etc. im not gonna go into details of the other roles bc were talking about chloroplasts but in short, chloroplast is a structure within the cells of plants or other photosynthetic eukaryotic that is the site of photosynthesis. you can search up the diagram of a chloroplast to better understand everything that is in it and how photosynthesis happens inside it