First of all, we should know that the composition of blood is plasma blood cells (white blood cells, red blood cells, platelets, granulocytes). Other white blood cells are mainly responsible for immunity, just like the police, and they turn to deal with necrotic cells or viruses and bacteria. High white blood cells indicate infection (viruses and or bacteria invade the human body! Red blood cells are mainly red blood cells that transport nutrients such as oxygen and carbon dioxide or body metabolites.
Platelets are like masons, so this is the meaning of blood collection (roughly understood)