Did you set up the target folder for the 'BaseFolder$' string variable in line 36? That will need to be changed to align with whatever the target '\media' folder is before it will know where to find the test and where to save the output file. You can also change it to some other location, but you'll need to include a file for it to perform encryption/decryption operations with if you don't use the included default file (and of course change the 'File$' value in line 262 to match).
As the included instructions indicate, you'll also want to edit the 'KeyBase[]' array values in lines 224-255 to apply whatever key value you want to encrypt your files with. Other details and instructions are included in the rem lines with the project.
From there, the code will utilize the standard AES256 encryption algorithm to encrypt and decrypt your files. Much like a protected ZIP system, it will output the results to a new file that you can then load or handle however you wish. If you want to just manage the data in memory, you can just transfer the memblock this system creates in the encrypt/decrypt functions over to a media file if you want to load them directly into memory without exporting an output file.