Sex is meant to be pleasurable. Pleasure is experienced by different people in different ways. People are aroused by a wide variety of images, smells, touch and feelings. Being touched, stroked, kissed on parts of your body that you find pleasurable or doing this to someone else can be arousing. Being sexually aroused triggers a range of physical responses. In both men and women the heart and breathing rate increases, blood pressure increases and skin may become flushed.
In most women and about 60% of men the nipples become erect especially on direct stimulation. The vagina produces lubrication, the clitoris swells, the breasts become slightly bigger and the lips at the entrance of the vagina increase in size. The penis gets harder, longer and wider. Continued stimulation will lead to increased pleasure, excitement and a desire to reach orgasm. Further stimulation may lead to orgasm, but this is also dependant on other things such as thoughts and feelings.