I want to know what is the difference between anemia and leukemia?

Different cells. Emia = blood. An-emia = lack of red blood cells (low hgb) associated with fatigue leukocytosis = more white blood cells (WBC) in the blood. One cause of leukocytosis is an increase in WBC cancer cell called leukemia.
A sign vs a disease. Anemia refers to a low red blood cell count and diminished capacity to carry oxygen. This has many causes. Leukemia is a cancer- a type of white blood cell growing out of control and preventing the others from doing their normal work.