How do I make the players arms and head follow the mouse?

I am making an FPS game and I want to know how I make the players head and arms follow the mouse, it's okay if the players head doesn't follow but I need the arms to follow so if the player looks down they can see so the arms aren't in the way, I have a script where the players arms are visible in first person. It's the player's real arms and not fake ones.