For those who have not seen and/or used (bad!) one, a condom is a thin sheath of latex or other material (for those allergic to latex), which is manually placed over the penis during erection. The tip has a small space that collects sperm, preventing their entry into the vagina. This is the only contraceptive method that protects against sexually transmitted diseases.
This method is cheap, does not require a prescription, does not require exams and can be used in conjunction with another method to enhance its effectiveness. It is recommended for adolescents during their first sexual experiences (when used along with a contraceptive pill, it offers 100% protection both against STDs and unwanted pregnancies), but its use is desirable in all situations of unprotected sex at any age.  It is easy to get one (pharmacies, department stores, supermarkets, vending machines, shops). It is easy to use starting from the first time. A condom is the most common barrier method, and is always necessary when "dancing with a stranger." Unfortunately, it is not always used correctly (hence there are numerous failures), and furthermore, young women don't always have the courage to ask their partners to use it... Not everyone has a positive experience with it; some people, both men and women, may experience allergies or intolerances.