The FPVFreerider_Data is a folder that contains the necessary files for the simulator.
You can find more general information in the user manual.
When you download the simulator here on Itch you will receive a zip file.
On Windows, you unzip that file to a folder of your choice.
In that folder, you will then find a FPVFreerider.exe file, which is the executable.
You will also find the user manual, as well as the FPVFreerider_Data folder, in the same place.
Usually you don't need to do anything with the data folder.