Typically ovulation occurs around day 14 of the menstural cycle but it can occur earlier or later. Ovulation is when an egg is released from your ovaries. Lutenizing Hormone rises thanks to estrogen output from the growing follicles, and it is this rise that triggers the events that now take place in the follicle.
LH makes the egg inside the follicle become fully mature, ready for release and fertilization. This is the point at which the egg reduces its number of chromosomes from 46 to 23.