Your doctor should have gone over the results with you in person or, lacking that, on the phone or at least by email. Leaving you to ponder a medical report written in "medicalese" and intended for doctors is not good service.
I'll do my best to interpret their lingo:
Normocellular Bone marrow
Your bone marrow is normal.
50%
The percentage of stem cells in a volume your bone marrow. The rest of the bone marrow consists of fat cells. When you are born it's almost 100%. It gradually decreases as you age, and when you are in your 90s it's about 10%. If you are in your 40s or 50s then your 50% cellularity is normal. If your are younger then it's a little low compared to the average. If you are older then it's higher than average. These are round numbers and being a little off the average may not be a concern.
maturing trilineage hematopoiesis
The immature cells in your bone marrow are maturing, as they are supposed to. You have three cell lines: red blood cells, white blood cells, and platelets, and all three lines ("trilineage") are maturing.
granulocytic hyperplasia
Among your white cells you have more than the usual number of the type called granulocytes. This can be a sign of inflammation or infection. The level rises as your body fights back, then should return to normal.
Decreased iron stores
You're low on iron (anemic).
The report is a summary, and your doctor can tell you if the results are "unremarkable" (as they say when you are fine) or if there's any sign that you need further testing.
A multi-vitamin with iron may indeed be all that you need, but your doctor should make that clear to you. We laypeople shouldn't have to make these interpretations ourselves.