index.php is basically the starting point for the web application (the main() function if you will).
qa-config-example.php has no function by itself. It's a configuration example that must be renamed to qa-config.php and filled with the desired configuration values. It's then sourced by other PHP files so that they have access to the config settings.
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask here, in English.
To report a bug, please create a new issue on Github or ask a question here with the bug tag.
If you just want to try Q2A, please use the demo site.
April 20, 2021: Q2A 1.8.6 released!