The primary function of red blood cells is to transport oxygen from the lungs to the cells of the body. RBCs contain a protein called hemoglobin that actually carries the oxygen.
A RBC has a strange shape, it's like a disc that is round and flat.
The size of A Red Blood Cell is 6-8 micrometers.
RBCs, depending on whether they are oxygenated or deoxygenated, can be any shade of red.

Red Blood Cells