Plugins etc... can use qa_usermetas for any meta information relating to users - see qa-db-metas.php. As for the other table, it's up to NoahY :)
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.