Testosterone is a hormone found in humans. Testosterone is produced by the testicles and the ovaries. The production of the hormones vary between different people. People with vulvas produce small quantities of testosterone as they are not the primary hormones responsible for fertility. Testosterone is a primary hormone responsible for the production of sperms and is responsible for the sexual development for people with penises. Low testosterone levels can lead to infertility.
Sources:
https://www.urologyhealth.org/urology-a-z/l/low-testosterone
https://www.healthline.com/health/what-is-testosterone#testing
https://www.medicalnewstoday.com/articles/276013
https://www.nih.gov/news-events/nih-research-matters/understanding-how-testosterone-affects-men
https://www.mayoclinic.org/healthy-lifestyle/sexual-health/in-depth/testosterone-therapy