Hi Umair,
Blood is made up of number of things. The 4 major components of blood are:
1) RBCs (Red blood cells or erythrocytes) I'm sure you are familiar with the function of these
2) WBCs(White blood cells or leukocytes) They seek out, identify and destroy harmful disease causing bacteria, viruses, and fungi. WBCs are an integral part of our immune system.
3) Platelets or thrombocytes are cells that release blood clotting chemicals at the site of wounds. They do this by sticking to the walls of blood vessels, thereby plugging the wounds and stopping the bleeding.
4) Plasma is the relatively clear liquid water, sugar, fat, protein and salt solution which carries the red cells, white cells, platelets, and all the other nutrients around our bodies through veins and arteries because these components don't move on their own and have to be floating in a carrying medium; which is plasma.