I have magento 2.0 C.E. And I want to override a few core template files. But, I do not have anything inside app/design/frontend/magento/ and my luma theme is installed somewhere in the vendor/ directory. I have not created any custom theme also. Please, let me know how this can be achieved.
I can give you a basic example.
Assume, if you want to override customer log-in form.
The original file path is from core.
Assume you need to do some customization. then copy the files to your theme, in this example take LUMA theme.
Then do necessary changes.