A good place to start is by skimming through the ever-growing list of frequently asked questions (with answers, of course). Then have a look at the rest of the online manual and other resources in the documentation section.
Books are convenient resources to begin exploring or extend your PHP knowledge. There are literally thousands of books available in English and numerous in other languages. Search at your favourite online or offline bookstore. You can search at Amazon.com, or go directly to Amazon.de or Amazon.fr and search there.
There are a number of mailing lists devoted to talking about PHP and related projects. This list describes them all, has links to searchable archives for all of the lists, and explains how to subscribe to the lists.
The PHP language newsgroup is comp.lang.php, available on any news server around the globe. In addition to this many of our mailing lists are also reflected onto the news server at news://news.php.net/. The server also has a read only web interface at http://news.php.net/.
Mailing list messages are transfered to newsgroup posts and newsgroup posts are sent to the mailing lists. Please note that these newsgroups are only available on this server.
Christopher R. Moewes-Bystrom is running a PHP user group registry at http://www.phpusergroups.org/. There's also a list of user groups in Germany, as well as news from them, and link to other countries user groups at http://www.phpug.de/. PHP Meetup is another great opportunity to get together.
A list of upcoming events (such as user group meetings and PHP training sessions) is included in the right-hand column of the front page, and on the event calendar page. If you want to list an upcoming event, just fill out the form on this page.
Otherwise known as IRC or Internet Relay Chat. Here you can usually find experienced PHP people sitting around doing nothing on various channels with php in their names. Note that there is no official IRC channel. Check OFTC or any other major network (EFNet, IRCNet, QuakeNet, IrCQNet, DALNet and freenode).
If you have a problem or suggestion in connection with the PHP.net website or mirror sites, please contact the webmasters. If you have problems setting up PHP or using some functionality, please ask your question on a support channel detailed above, the webmasters will not answer any such questions.