Questions tagged with tikz-pgf are about the higher-level drawing language TikZ built over the PGF graphics framework or about the whole TikZ/PGF stack. For questions specifically about the PGF layer use pgf-core instead. Both tags are possible on the same question.
In addition to all TikZ examples in questions on this site, TeXample.net shows examples of what can be done with TikZ.
For learning TikZ see: