To be completely honest the difference would be negligible. Just get in the gym and workout. From going from doing nothing to doing something your body will change and adapt fairly dramatically over the first few months. After that you need to up your game to keep the changes coming.

Diet? Providing yours isn't terrible at the moment why change? If you up colories it will counter the hard work you are trying to do to lose fat and if your not looking to be particularly muscular then no need on ramming loads of protein down your neck.

No doubt someone more deeply into the "you must do such and such at 15 seconds past 15.36hrs everyday" will come along and poo poo my advise. But lets be honest, train hard, eat well, rest, rinse and do it again! Thats it! Far too many people delve too deep into all sorts of theories etc. There is no substitute for hard work and consistency!