My serum iron level is 9 [range:14-28] ferritin is 18 [10-420] symptoms fatigue, headaches, dizziness do i need to use iron supplements/ferrous fumarate to increase it? whats the difference between serum iron and ferritin please?

Iron level is not a good marker for iron deficiency by itself. Ferritin reflects your body's iron but many conditions increase the ferritin level even you may be relatively deficient in iron. TIBC should be done to know if you truly have low iron. By those # I'd say you may have low iron but not 100% sure and without Hb/Hct/MCV/MCH/TIBC, I could not say if you should take iron supplement or not.

All laboratory results need to be interpreted in the clinical context and the doctor who ordered the tests is usually in the best position to do that. Talk to the doctor who ordered the tests. Having said that, your data is consistent with iron deficiency and you should take oral iron and multivitamin supplements to treat/prevent anemia. Wish you good health!