hardcore dancing and throwing down are the same thing. it refers to the dance that hardcore or scene kids do at hardcore shows. the time you throwdown is during the breakdown of the song.
two-stepping is done at the two-step of the song.
there are many variations of throwing down;
the windmill,
spin kick, pickin up pennies,
floor punch, ect.
the difference between throwing down and moshing is that you DON'T HIT EACH OTHER. it is non-violent (usually)
somtimes you'll see people purposely hitting each other, usually because one person is bad at throwing down, and they get knocked out of the pit because of it. alot of the time, if you ARE hit, it's accidental.
DO NOT HIT BACK! if you're hit in the pit, assume it was an accident. if you hit back, you'll get beaten. it's disrespectful and looked down upon to hit someone for hitting you in the pit. you'll end up getting gang beaten.