Transsexual

Transsexual people are people who change their appearance to more closely resemble that of the opposite sex. Transsexuals may be male or female. They typically take hormones and often undergo surgeries to support this process. They usually adopt a new name and may legally have their name changed. 

People who go from male to female (MTF) are referred to as transsexual women. People who go from female to male (FTM) are referred to as transsexual men.

Ways to go from male to female 
Transsexual women take female hormones. They may also take drugs that stop male hormones called androgens. Taking estrogen pills makes breasts grow. It does not make beards go away. It does not make voices higher. Transgender women may remove their facial hair so it does not grow back. This takes a long time and hurts. Some transsexual women with low voices have surgery to raise their voices. Other transsexual women try to make their voice sound higher and more female without surgery. Some transsexual women also get surgery on their genitals. This is called a vaginoplasty. This is done by making a vagina from the skin of their penis, which is turned inside out.  Some transsexual women also have surgery to make their faces look more feminine. Some also have surgery to make their breasts larger.

Ways to go from female to male 
Transsexual men take male hormones. This will make their voices lower. It will make a beard grow. It can also stop their menstruation. Some transsexual men look like any other man after hormones. 

Some transsexual men have surgery. One surgery is removal of breasts (mastectomy). Some transsexual men also get surgery on their genitals. One surgery is removal of the uterus and ovaries (hysterectomy). Some may also get surgery on their outside genitals. One way takes their skin and tissue and makes it into a penis (phalloplasty). Another way takes the clitoris (which grows bigger with hormones) and puts it where the penis usually is (metoidioplasty). The place where urine comes out (urethra) can be run through the new penis. The phalloplasty looks more like a penis. A metoidioplasty has more sexual function, but it is 5 or 6 centimeters long. Some ways also make a scrotum from the labia. They may also have the vagina taken out or closed.

Detransitioning 

Very rarely, some people (called detransitioners) who have changed sex decide this was a mistake and return to living as members of the sex in which they were born.
Some of the effects of surgery and hormones can be reversed but others are permanent.

Other websites 
 Gay and Lesbian Medical Association: Doctors who know about transsexual people.
 World Professional Association for Transgender Health (WPATH): Doctors, lawyers, and therapists who know about transsexual people.
 Tom Waddell Clinic  A clinic that helps transsexual people.
 Hormones for transsexual people: This helps doctors learn how to give hormones to transsexual people.

Notes 
 Note 1:  Lundstrom B, et al. “Outcome of sex reassignment surgery.” Acta Psychiat. Scandinavia. 70:289-294. 1984.
 Note 2:  Kuiper, M and Cohen-Kettenis, P. “Sex reassignment surgery: A study of 141 Dutch transsexuals.” Archives of Sexual Behavior. 17(5):439-457. 1988.

References

LGBT variations