While the VR mod is free, players will still need an official copy of Fallout 4 and the Fallout London mod. According to Fallout London VR's page, these are the necessary files to make it work.

Fallout London VR is a full virtual reality conversion of the best Fallout 4 mod to VR headsets, but only on PC.

Fallout London, the total conversion project for Fallout 4, gets a new mod that lets players explore post-apocalyptic England in virtual reality.