Do you only have the json files? Or are you using the program?
If you have the program you can click the install button. If you just have the json files, you have to place them manually.
Normally your game is located C:\Program Files (x86)\Steam\steamapps\common\Airport CEO
In there you go to \Airport CEO_Data\DataFiles
All businesses go in \Companies. All products sopd by franchises go in \Products