Both Steam and the site offer the same and only existing game version. Just don't reuse an old download, get a fresh one.
After installing, on the game startup splash screen, press the "Update" button so you get the latest updates.
You get two planes free: the Albatros DVa (Central side) and the Spad 13 (Entente side). So you can start exercising your flying and all that without paying anything.
There's immense value in the other (payed) planes and extras. But you can be happy for many months just flying the Albie DVa...
Before spending money in Rise of Flight, consider the fact that the company that produced this game is releasing the new game "Flying Circus" as part of the IL2 series. There are no freebies on this one, and it's still in pre-order (so even if you buy the pre-order you only get 4 planes to fly and will have to wait for the others). The game doesn't have a career mode yet, not even a WW1 specific map, although the latter has been announced. Just check here: https://il2sturmovik.../flying-circus/
Flying Circus will take some time to get all the existing features in Rise of Flight, although it has its own benefits, like 3D, improved plane models, etc. You may want to wait a bit and have fun in Rise of Flight in the meanwhile. Many people are doing that.
Here are the minimum system requirements from Flying Circus:
- OS: 64-bit Windows® 7 (SP1) / Windows® 8 / Windows® 10
- CPU: Intel® Core™ i5/i7 2.8 ГГц
- GPU: GeForce GTX 660/Radeon HD 7770 with 2GB VRAM or better
- DirectX: Version 11
- RAM: 4 Gb+
- Sound Card: DirectX®-compatible
- Storage space: 23 Gb+
- Internet connection: 256Kb/s for single-player career, 1Mb/s and faster for multi-player
- DirectX® compatible flight stick is recommended
If you have troubles, post here.