A cervix is a part of the vulva anatomy, It attaches the vagina to the uterus. Cervix is situated inside the vagina and is the lower part of the uterus. It is through the cervix that the menstrual blood escapes the uterus and passes out through the vagina. The cervix opening is narrow and menstrual products like a tampon or a menstrual cup cannot go through it.
Sources:
https://www.britannica.com/science/cervix
https://medlineplus.gov/ency/article/002317.htm
https://www.healthline.com/human-body-maps/vagina#conditions
https://www.verywellhealth.com/what-you-need-to-know-about-your-cervix-513843