Differences between the Metal Gear Solid V games

I have seen that for this month there is Metal Gear Solid V The Phantom Pain free for ps+ member. Now I have 2 questions:

1. There seems to be a definite edition with three games. ground zeros, phantom pain and a online thing. Can someone explain this to me?

2. While starting the game I got the question twice if I want downlaod some online data which is required to do some things.. i declined it twice.. can I downlaod those datas later? For what are they exactly for?