Adolescents and young adults are an important target concerning reducing health-risk behavior adoption, including sexual health. Studying their knowledge concerning sexuality and their main counsellors, can be an important step in targeting an updated health promotion approach. This study characterized adolescents and young adults’ knowledge and attitudes about sexually transmitted diseases (STDs), and contraception, prospecting for their main trusted counseling sources. We conducted a cross-sectional, population-based, self-report survey of 746 individuals aged between 14 and 24 years from Paredes, Portugal. The questionnaire included many dimensions, as demographic characteristics, youth behavior, currently sexually active status, main counselors concerning health topics, awareness, and knowledge about STDs and contraception. Mean age of the participants was 18.3 years, 50.5% of them had started their sexual activity. Males present themselves as more sexually active, starting earlier, and have more sexual partners than females. Participants reported an adequate knowledge perception about STDs and contraception methods, however we found different patterns on specific STDs and contraceptive methods, according to gender, age, and sexually active status. Our results help design specific interventions to reach youth, community, and healthcare providers, pointing out the value of bringing people to the center of health policies.