Resources

User Manuals

The official documentation http://www.qgis.org/en/docs/

Other Tutorials

http://docs.qgis.org/2.2/en/docs/training_manual/

http://www.qgistutorials.com/en/

http://maps.cga.harvard.edu/qgis/

Advanced Materials

QGIS API documentation http://www.qgis.org/api/

PyQGIS Cookbook for python programming in QGIS http://docs.qgis.org/testing/en/docs/pyqgis_developer_cookbook/

QGIS Plugin Development http://anitagraser.com/tag/plugin-development/