You will need to read the page about Single Sign On in order to let your Joomla users use Q2A. Follow the instructions in qa-external-users.php to return appropriate data from the functions.
You can find instructions for dealing with Joomla users outside of Joomla by searching Google.
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.