Like other primates, Homo sapiens uses sexuality for reproduction and for maintainance of social bonds. Even as our other behaviors, our high intelligence and complex societies have produced in us the most complicated sexual behaviors of any animal.
Most people enjoy some sexual activities, however most societies have defined some sexual activities as inappropriate (wrong person, wrong activity, wrong time, etc.) Many sexual activities can be engaged in by partners of either sex, however some, (most notably sexual intercourse), can only be engaged in by partners of opposite sexes.
Most people have a few specific sexual activities that they particularly enjoy, though most people have experimented with a range of sexual activities at one time or another. Some people enjoy many different sexual activities, while others avoid sexual activities altogether for religious reasons or by personal preference (see abstinence).
Problems may occur when a person particularly desires a particular sexual activity, but a temporary or long-term partner does not. Rules of etiquette similar to those of other areas of social activity seem to apply: Being pushy is generally rude; try to indulge your partner's desires if you feel comfortable with doing so, but not to the point you feel taken advantage of; honesty is generally a good policy but can be taken to extremes. In cases where a difference in desire for a particular activity is causing problems, counselling can be helpful. Note that some activities are actually illegal in some jurisdictions.
Many people enjoy fantasizing about, or reading or viewing depictions of, sexual activities that they do not wish to engage in in their own lives, or that they would be unable to engage in in their own lives (see pornography and erotica). Some people engage in various sexual activities as a business transaction; this is called prostitution.
Common sexual activities include:
Generally less common are the various paraphilas
All sexual behaviors that result in the contact of semen with the vagina or vulva may result in pregnancy at any time unless adequate contraceptive (birth control) measures are in force. Sexual intercourse is generally a very effective cause of pregnancy and should be avoided (see abstinence) unless either pregnancy is desired or adequate contraceptive measures are in force.
Note that all sexual behaviors that involve contact with another person or the body fluids of another person should be considered to contain some risk of transmission of sexually transmitted diseases.