I've created an application which will demonstrate how ransomware works. It will create a new folder on your desktop with files.
After that you can decide if you already want to encrypt the files, but you could also change their names or their content.
If you encrypted your files, the content will look like complete gibberish. Not really readable and not revertable.
After you encrypted your files or if your files already are encrypted ( the application will only detect that scenario if every file is encrypted ) the program will ask you if you want to decrypt them afterwards. Making their content readable again.