Part 1 is the free stuff. If you download this and play it, it will stop after a certain point and ask you to buy part 2. Part 2 has part 1 built-in and you don't need to do anything special. Just play and it will seamlessly continue all the way to the end. There's no special screen or anything that says "Part 2 begins here". It will just continue. If it helps, I think part 1 should've been renamed as Demo version and part 2 should've been named as Full Version.