SRS stands for "sex reassignment surgery", and is the surgical correction of genitalia so that they approximate the appearance and function of genitalia of the other sex.
It is also known as GRS (gender reassignment surgery), GCS (gender correction surgery), or "bottom" surgery (to distinguish it from "top" surgery, i.e. breast augmentation, facial surgery, and vocal surgery).
I have found it helpful to think of gender body dysphoria as basically a birth-defect in which the body is shaped according to a different program than that which shaped the mind, and SRS as the correction for that defect. (Even if one wanted to tinker with one's brain at the very deep levels of identity that are involved with this, there is at present no known remedy nor even any likely research leads other than better understanding of how intelligence works.)
For male-to-female SRS, the appearance is generally quite similar to the naturally-grown variety, to the point where medical professionals may assume that a surgically-created vagina is in fact original equipment (biologically created).
I have posted a great deal more information on HTYP.