I often find bugs in QGIS and its Plugins.
I would like to ask about this on the internet but I do not seem to find the proper place to address this issue.
Are there any instructions?
For QGIS, see http://hub.qgis.org/projects/quantum-gis/issues
For plugins, see http://hub.qgis.org/projects/qgis-user-plugins/issues
You need an OSGeo account to fill tickets. After creating that, go to your OSGeo user page. Then you can login to hub.qgis.org with the same user ID.