http://www.chess.com/learn-how-to-play-chess.html
CASTLING CONCERNS

yep! The previous link describes castling fully and clearly (don't try to add limitations to the business like worrying over a Rook being under attack, besides, the site won't let you make an illegal castling move):
- it must be that king’s very first move
- it must be that rook’s very first move
- there cannot be any pieces between the king and rook to move
- the king may not be in check or pass through check

- it must be that king’s very first move
- it must be that rook’s very first move
- there cannot be any pieces between the king and rook to move
- the king may not be in check or pass through check

the scp[aces between the king and rook cannot be threatened either?
True for a king side castle, not 100% true for queen side. This is because what matters is the king not "going through" a threatened square. With a queen side castle, the square next to the rook may be threatened, and it's still a legal move.
Could someone please explain in detail all the different rules that aplly to CASTLING? I know you can't castle out of check, what about if the rook is threatened?
P.S. FRIEND REQUEST ME!!!!