Plone has a strong, vibrant, and active community. There are many options to get help if you are stuck in the middle of something. Let's see what you can do:
Documentation on plone.org
Google and blogs
Mailing lists / forums
IRC (online support)
Commercial support
The documentation on the plone.org website is probably the number one place to start if looking for Plone-related help. The site itself is Plone driven and comes with the familiar fulltext search.
There is a special documentation section where you can find categories for all kinds of Plone-related topics. These include:
Basic use
Configuration and setup
Managing content
Users, authentication, and permissions
Upgrading, moving, and so on
Each document entry has information attached about which Plone version it is applicable to and what is the targeted audience: end users, site administrators, or developers.
Not all documentation is hosted on plone.org itself. A good deal of it is widespread over different blogs, private websites, and various other web resources. Search engines such as Google are a big help here.
There is a news collector at www.planet.plone.org. Everyone who is running a Plone-centric blog may register there. You can subscribe to the provided RSS syndication feed as a whole or to the RSS feed of individual participants.
The Plone community maintains a couple of mailing lists for the discussion of relevant topics. These mailing lists are mirrored as forums on http://plone.org/support/forums. All the entries can be read there.
There are several ways to post to these lists/forums. One option is to have a Nabble account (http://www.nabble.com/). Another option is to subscribe to the mailing lists through Gmane (http://gmane.org/) with your favorite mail client.
The most important lists are probably:
Plone User: A list of questions for people using the Plone CMS. This list is the most active one and it is OK for a newbie to ask questions there.
Plone Developers: The list for Plone core developers. On this list, possible new features and problems with current ones in the Plone core are discussed. It is for the core developers only.
Plone Product Developers: The list for add-on products. Questions and topics related to third-party products and extensions are discussed on this list.
Note
Always remember to check the documentation on plone.org and other resources before asking any questions. Try to include as much information as possible (Plone version, operating system, installed products, and error traceback). Most of the communication rules listed in the online support part apply here too.
Plone4Artists used to have its own website, but it seems to be gone. It still has its own mailing list, which is hosted on Google groups: http://groups.google.com/group/p4a-user.
To get real-time support, it is possible to use an IRC (Internet Relay Chat). On irc.freenode.net, there is a dedicated Plone channel: #plone. It can be accessed directly through the Web or with a dedicated chat client. Information on working chat clients can be found at http://plone.org/support/chat.
The chat is a volunteer service. There is no guarantee that your question will be answered. Here are some tips from plone.org to enhance your chance of getting help:
Don't ask if you can ask a question—just ask it.
Tell what you're trying to achieve, what you're doing, and what's not working.
Being polite is the best way to get the help you need.
Do your research before you ask questions. Use other means of getting help before asking.
The level of activity varies, so if you don't get help at once, stay online for a while. (Most chat participants are on North/Central/South America or European time, and tend to be most active during normal business hours.) People will answer if they know, or ask for more details if they need it. Repeating the same question again and again won't help.
Don't send private messages to people unless they have asked you to.
Don't paste code into the chat room—use a paster service (such as pastie.org) and paste the URL of the result to the channel instead.
Another option is to enlist a professional consultant. On plone.net, there is list of Plone providers for several countries. This list includes hosting, development, and other consultant service providers.