Corrected sentence: The right side of the heart collects blood that doesn’t have much oxygen and sends it to the lungs.
Even simpler: The right side of the heart sends blood that needs oxygen to the lungs.
Explanation for a 5-year-old: Your heart is like a pump. The right side takes blood that needs oxygen and sends it to the lungs. The lungs give the blood oxygen, and then the blood goes back to the heart so it can travel to the rest of the body.