RBC: carry oxygen, no nucleus (function via diffusion or osmosis), are biconcave and thus can stack and travel through narrow openings, smaller then WBC and are more plentiful. I think they make up 99.5% of our blood.
WBC: bigger, have nucleus (need energy), subdivisions: leukocytes monocytes erythrocytes (these are agranular) basophils neutrophils (granulated). Defenders of your body, protect against pathogens and foreign bodies. Also play role in cancer defeating and in blood clotting.