So there are several different "levels" of female circumcision, the least invasive is the removal of the clitoral hood, which is most analogous to male circumcision. The most invasive procedure involves the complete removal of the clitorus and labia, and the vagina is almost completely sewn shut aside from a small hole to allow for her period to bleed through. Like I said, there are many levels and each level is indicative of a different procedure.

As for why its done, there's no supposed health benefit to it like male circumcision (whether there is any actual health benefit to male circumcision is a whole different question, but supposedly it decreases the risk of infection) and its primarily done to control women and ensure they receive no pleasure from sex