QGIS has a bunch of mailing lists. See Mailing lists for the different available lists.
If you are going to ask questions please read this: How to ask a QGIS question?.
Nabble (http://nabble.com) keeps a history of a lot of mailinglists.
If you go to the osgeo section of it: http://osgeo-org.1560.x6.nabble.com/ you see there is a QGIS section also, where you can do a search over all QGIS lists, or refine it to e.g. only the users list.
On http://gis.stackexchange.com you can ask QGIS questions also. If you use the
tag qgis you’ll see all QGIS related questions and answers:
http://gis.stackexchange.com/?tags=qgis
A lot of the development buzz will be spoken on IRC.
There is a #qgis channel on freenode.net. You can also use a web interface: http://webchat.freenode.net/?channels=#qgis If you missed a discussion on IRC, not a problem! We log all discussion, so you can easily catch up. Just go to https://qgis.org/irclogs.
Local QGIS user groups are a great place to meet other users.
See User Groups to read about it.
The website should be used to publish any material in relation to the information and management of the user group. Examples include the user meetings, case study, shared material, discussion boards, etc. Public material should be available without login requirements (e.g. do not require interested people to be a member of a social media network like Facebook or Google+). Usage of social media is recommended but should not be the only channel of information. RSS feeds should be made available at the Website of the QGIS user group.
Good luck with the organization of your local user group. Please inform the international QGIS team by registering at the QGIS community list and reporting about your progress. Please do not hesitate to ask questions regarding the establishment and maintenance of your local user group.
If you want to file bugs or issues, see Bugs, Features and Issues.
You can also get support from companies near you, please visit this page: Commercial support.
QGIS does not have a forum. Please either search in StackExchange (see below), or via http://nabble.com in the history of our Mailinglists (see above).
For non-english, note that there also exist local forums that have a dedicated section for QGIS you may need to search in.