What are the signs of having anemia?

Weakness. Anemia is a lack of red blood cells, and that means less oxygen is delivered to your body per heart beat. The heart compensates by increasing heart rate. Symptoms include feeling cold, lightheaded or dizzy, being fatigued, and getting fast pulse rate and shortness of breath with only minimal exercise. Anemic people appear pale. Other symptoms depend on the cause of the anemia.
Signs & symptoms... Include fatigue, exercise intolerance, headache, pallor, etc. Therapy depends upon the underlying cause, and causes of anemia are many and varied. They can result from impaired rbc production (eg., nutritional deficiencies, marrow infiltration, etc), hematoma, blood loss (gi bleed, hemorrhage, epistaxis, etc.), hemolysis, thalassemia, hemoglobinopathies, etc. More specific info would help.