You have probably been directed to this page by a channel topic or join message. It's usually best to consult here if you have questions like why people use [[wikilinks]] in chat or why publishing channel logs will result in permanent banning.
Can I publish logs of the channel? 
No. Doing so may result in being permanently banned. This policy is explained more fully on the IRC channels page--questions and discussions about the policy should be directed there.
Scripts exist for some IRC clients to enable clicking on [[wikilinks]]; they are available at w:Wikipedia:Scripts. Since typing such links is so much more convenient than typing out full URLs, they are almost invariably used. If your client does not have a script, you can always paste the text between the [[ and ]] into the search box.
Why did I get disconnected? 
There could be a lot of reasons, but you should check to make sure you aren't using a wireless router affected by CVE-2006-1068, which causes the router to disconnect when certain strings containing "DCC SEND" are used on IRC. Troublemakers use this vulnerability to disconnect people from IRC. Please connect to freenode on port 8001 rather than 6667. This will prevent you from being disconnected, and discourage the troublemakers by removing their targets.
How do I ask for help/an answer? 
Politely. In general it's much more effective to just ask your question or state the situation you would like addressed, rather than asking if there is an admin around, or if there's someone who can help you.
Can I paste long excerpts in the channel? 
It's preferable to use a paste service like p.defau.lt instead, and link to it.
What do the channel modes mean? 
Channel modes for freenode are explained in their documentation. Freenode uses a custom IRC server with some extended modes.
Who are the operators? 
You can view a live list of channel operators by querying chanserv with the command:
/msg chanserv access #wikipedia list
For other channels, replace #wikipedia with the name of the channel. For an on-wiki list of Wikipedia channel operators, see IRC/wikipedia/Operators.
I'm banned from the channel, and I didn't do anything. What do I do? 
Most likely, someone (or some large group of someones) from your ISP, or someone who has a nick like yours, got banned for good reason, or you're using a proxy or web gateway that is banned from the channel. Head into #wikimedia-ops and see if someone can get you straightened out.
I got banned for something I did, but it wasn't fair. What do I do? 
Message the op who banned you. Ask why you were banned... and be polite, even if you think it was unfair; ranting never helps. If that doesn't help, try #wikimedia-ops, and make your case calmly.
Is #wikipedia an official Wikipedia channel? 
No. It's a gathering place for Wikipedians, and many experienced users are ops in channel, but anything you hear there should be taken with a grain of salt. It could be coming from a Board member, but it could also be coming from a newbie who found the site five minutes before you did. The Foundation does not monitor or control what goes on there.