Can anyone explain me the different dosages of homeopathy in order from low to high and their usage ?

Very broad question: Classical homeopathy can be used in almost any kind of illness -- sometimes as primary treatment, and sometimes in conjunction with conventional treatment. Homeopathic medicines ("remedies") number in the thousands, and are made from mineral, plant, or animal substances found in the natural world. Potency used depends entirely on the patient & presentation -- match to pace & depth of experience.

Dosing schedule: Remedy doses are generally available at low potency 3x, 6x, 12x, or 12c potencies for example. Medium range is typically 30c or 200c. Higher potencies are usually 1m ( or 1000 c) or 10m. In certain cases, a trained homeopath may need to repeat the remedy at even higher 50m. The proper dose to rx requires in depth training.