Iron is an important constituent of hemoglobin and is necessary for oxygen transport to various body tissues. Iron deficiency is a common cause of anemia, especially among children, women of childbearing age and pregnant women. If your levels are low then it can be rectified by eating iron supplements (as advised by your physician) or even by adding iron containing foods in your diet (apples, beetroot, green leafy vegetables like spinach, pomegranate & meat/poultry etc.).
Ferritin is a protein that stores iron. Ferritin level in blood indicates the total level of iron stored in the body, and its derangement may be suggestive of iron deficiency anemia, iron overload, liver diseases and certain syndromes. Think of ferritin as your bank & serum Iron as your wallet. The levels in your wallet might be fluctuating but any changes are ferritin happen over a longer time. Ferritin also acts as an acute phase reactant & might be elevated in cases of inflammation in the body. Hence it is always recommended to interpret the value of ferritin keeping in mind any causes of inflammation in the person's body.
It measures the total iron binding capacity in blood.
This test measures the reserve iron binding capacity.
Transferrin is a protein that binds with iron and helps in its transport. Transferrin saturation is the percentage of transferrin attached to iron as compared to the maximum transferrin available to bind with iron.