Animal cells don't have chloroplasts because animals aren't green plants. Chloroplasts are organelles, or small, specialized bodies in plant cells that contain chlorophyll and help with the process of photosynthesis. Like mitochondria, chloroplasts have their own DNA.
Chloroplasts come in various shapes, with many of them shaped like disks. They have an inner and outer membrane. The inner membrane surrounds and protects stacks of thylakoids, which are called grana and the stroma. Stroma is an alkaline, nutrient-rich fluid. It also contains the chloroplast's DNA, ribosomes and starches. The grana connect to each other by stroma lamella, which keep them in order and allow them to perform photosynthesis more efficiently. Molecules of chlorophyll reside on the surface of the thylakoids.
When the chlorophyll molecule in a chloroplast absorbs sunlight, the molecule gets excited and loses an electron. This gives it a positive charge and allows it to grab electrons from other substances, including water. This destabilizes the water molecule, which decomposes and releases oxygen and hydrogen. The oxygen is the plant's waste product, which humans and other animals use to breathe. The plant uses hydrogen to convert carbon dioxide into simple sugars. This CO2 fixing happens in the stroma and is the basis of photosynthesis.