Sharpen is a post process visual filter that makes everything, well, sharper. While you're at it, note the new graphics options there: Sharpen and Dynamic resolution factor. If VR still won't kick in, go to graphics settings of the game and check that 'Use VR HMD' option is on. If you launch IL-2 and VR mode doesn't kick in, make sure that Steam VR (and Oculus Home if you have Oculus Rift) are installed and configured properly, and/or launch them manually before starting the game.
Oculus Home and Steam VR windows may obscure the IL-2 window on your regular monitor so minimize them and click on IL-2 Sturmovik window to return focus to it (that's how Windows works) When the game loads, your HMD should be working already and you should see the VR image from one of the eye screens on your regular monitor. If Oculus Home and Steam VR applications are not active, it should launch them by itself. Make sure it works fine for you in Steam VR tutorial. Run Steam VR to set up your Oculus Rift there: run Room Setup. So, the first step would be installing Steam, logging into your Steam account and installing Steam VR from Steam store.
However, if you have Oculus Rift, you may or may not have it installed. If you have HTC Vive, it is already installed (or you won't be able to use it in other games). IL-2 Sturmovik uses Open VR interface, meaning you need to have Steam VR application installed on your PC. Here are some tips & tricks you may already know that will help set up your VR for IL-2 (but it may be useful for other games).