When adding my application to Windows right-click menu

[Yesterday Paid]

I made a cipher app but to make easy, I want to make it Windows
rightclick menu can execute it
I found the way with dealing with Registry


[HKEY_CLASSES_ROOT\Directory\Background\shell\app]
 [HKEY_CLASSES_ROOT\Directory\Background\shell\app\command]
 @="C;\myapp filelocation"


but I don't know how to automatically get filelocation
Can I get the address of file that I right_clicked(it's not a proper
expression maybe)