We can see this by observing animals' sexual behavior. But, obviously, humans' behavior is different and much more complex than that of animals, even when the biological aspects of it are very similar to those of mammals. The secretion of androgens is constant in the short run, and that is why men can engage in and demonstrate interest in sexual activities without regard to any biological cycle, given the stimuli to generate excitement.
Women have a more complex system of behavior.
In puberty, the two ovaries produce estrogen and progesterone. This production is not constant, but follows a cyclic pattern. The most production takes place during ovulation, when an ovule is separated. Unlike animals, humans can be sexually excited, not only by the presence of a partner, but also by many other stimuli. The reaction one may have to a certain stimuli is absolutely personal.