What is meant by "the virgin does not perform ghusl until semen emerges from her vulva," and is it meant by this that it is seen on her underwear, and is semen like water or does it have another consistency?

A virgin is not required to perform ghusl (ritual bath) unless semen exits to the outer part of her vulva, not merely reaching her underwear. This is because the inner part of her vagina is considered to be like an internal organ. Semen has specific characteristics that distinguish it from other discharges.