One of the joys of chat is the immediacy of IRC. So here's a quick guide for your basic IRC commands.
Choosing a client
In addition to web-based services, there are many programs available, some of which are listed on Wikipedia (with more included in this list as well). If you already have a program that allows you to chat in AIM, MSN, and Yahoo all at once, you might already have an IRC program.
Commands
Server: /server irc.synirc.net
This will connect you to the chat network.
Nick: /nick newnick
This is basically your username. Start with IntenseDebate name, to make it easy to be identified. If you want to change your nick, you can do this at any time by using the above command.
Register: /msg NickServ register PASSWORD EMAIL
With PASSWORD being replaced with your desired password, and EMAIL being replaced with your working email address
Nick registration isn't complete until you send the command found in the registration email you'll receive.
Identify: /msg NickServ identify PASSWORD
With PASSWORD being replaced by your actual password
When you've registered your nick, this will tell NickServ you are who you say you are.
Channels: /join #MarkSpoils
This is how you join the Mark Spoils channel. If you wish to join other channels, type /join #channelname
Some programs automatically assume the # symbol before the channel name; if you join a channel you expect to be full and find it empty, check the channel name. If it says ##channelname, leave and use the join command again, without the # symbol.
Query: /query nick message
A query is a private chat. Using this command will open a new window within the program.
A lot of programs will simply let you double-click on a user's nick to open a p2p with them. Try it; it's fun!
Terminology
Op (OP): This is a short version of saying channel operator. These are the moderators of the channel, who can kick people out or ban them for misbehavior. Most programs will put these people at the top of the nick list (where you see the names of everyone in the channel), and many will differentiate them with some sort of symbol (it varies, but the @ symbol is common) or different color. You might also see op used as a verb; this means setting someone as a channel operator.
p2p: Stands for peer-to-peer and is another way of saying a query. Often people will ask to p2p something to you or want to open a p2p with you.
Netsplit: IRC services are made up of several servers; sometimes these servers fail to communicate. What happens is a netsplit. It will look like a number of people quit at the same time. Within a minute or two, those people will come back all at once. It's not a big deal, but it can be amusing to watch.
Updated July 21, 2015.