Separate Ways is an unlockable item or more like an unlockable mode in RE4 wherein you get to Play from Ada's Prospective and make your way through the village till the end.Its more like revealing a lot of Ada's side of the story for those who were left confused with Her brief appreance in RE4 while playing as Leon.For all of this and other goodies to be unlocked just complete the whole game.By the end you'll have The Professional difficulty mode,The mercenaries mini game,Assignment Ada,Separate ways and If I remember correctly then there was this movie browser mode wherein you could view all the Cut Scenes which occured during the game.