FSH or the follicle stimulating hormone, from the name itself, stimulates the growth of the follicles and the eggs in the ovaries, specifically the granulosa cells. FSH is also responsible in stimulating estrogen production in the ovaries.
LH or the luteinizing hormone, on the other hand, acts on the theca cells of the ovaries which stimulates further estrogen production. Estrogen, also stimulates the production of LH (positive feedback mechanism) thereby leading to a spike or sudden peak in LH production which triggers ovulation.