Not sure exactly which bits you already understand. Also, I'm not a doctor: I teach medical students stuff like this.
HbA1c (glycated haemoglobin) - indicator of long-term control of blood glucose concentration. Should be below 48 mmol/mol in well-controlled diabetes and below 42 mmol/mol in people at risk of developing type-2 diabetes. You are well below that level.
Vitamin B12 - molecule required for normal replication of DNA, and therefore for normal cell proliferation. Deficiency is associated with megaloblastic anaemia, in which growing red blood cells (erythrocytes) can't divide properly and therefore you get reduced numbers of large cells that don't function properly. Vitamin B12 requires a substance called intrinsic factor (IF) to facilitate its absorption from the small intestine. IF is secreted by cells in the stomach (the same cells that secrete hydrochloric acid). A particular form of autoimmune gastritis damages these cells and/or neutralises IF, thereby resulting in reduced IF availability and impaired B12 absorption (pernicious anaemia). Normal range is a bit vague: levels below 150 pmol/L (approx 200 ng/L) might be recommended to be investigated, but the bottom of the normal range is 115 pmol/L (approx 155 ng/L - the lab has rounded this up to 160 ng/L). Your result is within the normal range but some people with your levels do experience symptoms.
T4 and T3 (thyroxine and triiodothyronine) - thyroid hormones. Responsible for regulation of basal metabolic rate and other cell functions. Normal ranges are free T4 12-22 pmol/L and free T3 3.1-6.8 pmol/L. Your T4 is slightly low. In itself, this doesn't tell you much. Diagnosis of thyroid or pituitary problems would be based on TSH levels.
TSH (thyroid-stimulating hormone) - hormone released from the anterior (front) pituitary gland that regulates thyroid hormone secretion. Normal range is 0.27-4.2 mIU/L. Yours is right in the middle of the normal range. If you were hypothyroid you would expect it to be high; if hyperthyroid, you would expect it to be low. This is because of a feedback loop through which thyroid hormones inhibit the secretion of TSH, so high thyroid hormone levels lead to low TSH, etc.
Ferritin - protein that stores iron, mostly in the cells lining the small intestine (intesitnal epithelial cells, or enterocytes). Patients with iron deficiency will usually have low ferritin as they use up their stores to make haemoglobin. Normal range in adult females is 10-300 ng/mL, so you're comfortably within this range. What might be more important is whether it is going down over time, which would suggest you're using up iron stores.
Haemoglobin - molecule in red blood cells that carries oxygen. Normal range in adult females is 115-165 g/L, so again you're well within the normal range.
White blood cells (leukocytes) - cells involved in immune defence. Normal range is 3.6-11 x 10^9/L. Higher levels would usually be associated with infection. Lower levels might indicate bone marrow suppression, which might have a variety of causes. Again, you are within the normal range.
Nothing here that looks out of the ordinary. The B12 is on the low side of normal but haemoglobin is normal, so unless there is something else abnormal (e.g. high mean corpuscular volume [MCV]) there isn't really anything to suggest megaloblastic anaemia.
I'm presuming these tests were performed because you are feeling fatigued, and possibly breathless, so the doctor is probably trying to rule out possible causes as much as to confirm a diagnosis.
Repeating caveat: I'm not a doctor; I'm just telling you what the tests are.