Male to female transition surgery involves cutting open the scrotum between the gonads and removing the gonads. The lower side of the penis is cut open and it is used to create the new vagina, and the scrotum for the lining. Female to male transition involves a mastectomy and a penis is created. Some transmen may still have a uterus (a transman in the USA gave birth to a baby in this way).

Some transphobes carry on and say a transwoman is biologically a man. The chromosomes don't change, so a transwoman still needs PSA checks and the like.

The best way to think of gender dysphoria is, you bought a 1970s model car in the 1980s and it had an AM radio with two speakers, and you wanted to upgrade to have an AM/FM radio and cassette player. The head unit you bought had a 35 watt output and the speakers in there were 15 watts, so, if you connected the head unit to the speakers, they'd go, "No way!" and break. So, gender reassignment surgery is a matter of changing the body to suit the brain.