Airsoft is largely based on the honor system. Depending on rules
used for each round, most of the time if you're hit anywhere you're
dead. Once you're hit, you shout "HIT!" loudly, put yr hands up in
the air and stand up. As you go back to respawn shout "dead man
walking" so people know u're dead. Generally hits to any part of
your gear or you counts as hits. Some sites consider weapon hits to
be hits, others don't. There are also bang rules, tag rules as well
as surrender rules, which govern close quarter engagements. Also
most sites have marshals to make sure people take their hits and
ensure fair play.
As for whether it hurts, it depends on how close you are to the
opponent when he fired at you. Generally, yes, it hurts a bit, but
not that much really. Being a girl myself, I say that since I can
stand the pain of getting my eyebrows plucked, airsoft hits are
nothing.