What sexual intercourse is — a straightforward explanation

Sexual intercourse (often shortened to "sex") generally refers to physical sexual activity between people that involves genital contact and/or stimulation. For many people the most common meaning is vaginal penetration by a penis (penile-vaginal sex), but the term is also used more broadly to include oral sex, anal sex, and other kinds of sexual contact between consenting adults.

Key anatomy (basic terms)

• Penis: external male genital organ. Erection is the physiological response that makes penetration possible for many people with penises.
• Vagina: internal female genital tract leading from the external vulva to the cervix and uterus. Vaginal intercourse refers to insertion of a penis or object into the vagina.
• Clitoris: small but highly sensitive organ on the vulva important in sexual pleasure for many people with vulvas.
• Cervix and uterus: internal reproductive organs; fertilization and pregnancy involve these structures in penile-vaginal sex when contraception is not used.
• Other contact: mouth (oral sex), anus (anal sex), and other erogenous zones can all be involved.

Typical step-by-step sequence (physiological and behavioral stages)

People’s experiences vary widely. The following is a neutral, clinical outline of common stages rather than a prescriptive checklist.

1. Attraction and desire: feelings of sexual interest can arise from emotional closeness, physical attraction, fantasy, hormones, or social/contextual cues.
2. Consent and communication: before any sexual contact, clear and freely given consent from everyone involved is essential. This includes discussing boundaries, safer-sex practices, birth control, and STI status. Consent can be withdrawn at any time.
3. Foreplay and arousal: kissing, touching, massage, caressing, oral/genital stimulation, and other behaviors increase physical arousal. Physiological responses include increased heart rate, genital blood flow (erection for many penises; swelling and lubrication for many vulvas), and mental/emotional readiness.
4. Preparation and protection: before penetration, many people use protection — condoms (male or female), lubricant, dental dams for oral sex, or agreed-upon contraception (pill, IUD, implant, etc.). Lubricant reduces friction and can prevent tearing. If pregnancy is not desired, reliable contraception should be in place.
5. Penetration or sexual contact: if the partners choose penetration (vaginal or anal) it is entered gently and usually paced according to comfort. Sexual contact may also be non-penetrative (mutual stimulation, oral sex, etc.). Good communication continues about comfort and preferences.
6. Stimulation, rhythm, and feedback: partners typically adjust movement, speed, depth, and type of stimulation based on verbal and nonverbal feedback to increase mutual comfort and pleasure.
7. Orgasm and ejaculation (may or may not occur): orgasm is a peak of sexual pleasure that can involve rhythmic muscular contractions and intense sensations for many people; ejaculation is the release of semen for many people with penises. Not everyone orgasms during intercourse, and that is normal.
8. Resolution and aftercare: after sex, people often experience a relaxation phase. Emotional aftercare—talking, cuddling, checking in about how each person felt—is important. Clean-up and attending to contraception or emergency contraception (if needed) may follow.

Different forms and safety considerations

• Vaginal sex: carries risk of pregnancy and sexually transmitted infections (STIs) if protection is not used. Use condoms plus another contraceptive method for highest STI protection plus pregnancy prevention.
• Anal sex: higher risk of some STIs and of tissue tears; condoms and lubrication are strongly recommended.
• Oral sex: can transmit STIs (e.g., herpes, gonorrhea, HPV). Dental dams or condoms can reduce risk.

Protection, contraception and sexual health

• Condoms: reduce risk of most STIs and pregnancy (when used correctly).
• Hormonal methods (pill, patch, ring, injection), IUDs, and implants: effective at preventing pregnancy but do not protect against STIs.
• Emergency contraception: effective after unprotected sex to reduce pregnancy risk; time-sensitive.
• Regular STI testing and open discussion of sexual history are important parts of responsible sexual health.

Why do people have sex? (main reasons)

• Reproduction: biologically, one function is producing offspring.
• Pleasure: physical sensations and orgasms are strong motivators for many people.
• Intimacy and bonding: sex can strengthen emotional connection and release bonding hormones like oxytocin.
• Stress relief and mood: sex can reduce stress and improve mood for some people.
• Exploration and identity: people use sex to learn about their bodies, desires, and orientation.
• Social or cultural reasons: relationships, partner expectations, curiosity, or social status can play roles.

Why is sex still a taboo in many places?

Sexuality is still taboo for many reasons—often a mix of historical, cultural, religious, and political factors:

• Religious and moral beliefs: many religions have rules about sexual behavior, which shape cultural norms and taboos.
• Historical control and power: laws and social rules around sex have been used to control reproduction, gender roles, and minority groups.
• Privacy and intimacy: sex involves very personal parts of life; many cultures consider it private rather than public conversation.
• Gender norms and shame: people—particularly women and LGBTQ+ people—have often been stigmatized for sexual behavior, creating silence and shame.
• Lack of education: when people don’t receive open, accurate sex education, myths and fear tend to fill the gap, reinforcing taboo.
• Fear of changing social order: open discussion of sex can challenge existing family structures, power dynamics, and traditional values, which some societies resist.

Practical, responsible tips for a 20-year-old

• Always seek clear, enthusiastic consent and respect boundaries.
• Use condoms to reduce STI risk; if you want to avoid pregnancy, also use a reliable contraceptive method.
• Get regular STI testing if you’re sexually active with new or multiple partners.
• Communicate with partners about preferences, limits, and sexual health.
• Educate yourself from trusted sources—clinics, sexual health organizations (e.g., Planned Parenthood, WHO, CDC), or healthcare providers—rather than relying on myths or pornography.

Where to learn more

Trusted resources include local health clinics, university health services, and reputable organizations like Planned Parenthood, the Centers for Disease Control and Prevention (CDC), and the World Health Organization (WHO). If you have specific medical or legal questions (contraception choice, STI symptoms, age-of-consent laws), talk confidentially with a healthcare provider or counselor.

If you want, I can point you to specific articles, explain contraception methods in more detail, or discuss how to talk about consent and boundaries with a partner.