Instant Messaging is a technology that lets you send and receive short text messages directly between computers. But as opposed to text messaging on phones, where you just see one message at a time, your IM program (or "client") shows you all your messages to and from each friend in a list, so you can carry on a constant conversation.

An IM client, showing my list of buddies

After Mirabilis essentially created the Instant Messaging client with ICQ (AOL and other services had had IM before, but it was always walled off within a proprietary service), several different IM clients emerged. Each one is popular in different parts of the world.

AOL Instant Messenger, or AIM, is the most popular in the United States. Canadians seem to love MSN Messenger, while ICQ is still very popular in Russia and Europe. Yahoo! Messenger has a lot of users in South America, I believe. Jabber is also broadly popular; it's not run by one huge company.

Fortunately, all of these services are free, and there are ways to use several at once, if you need to.

They all work in basically the same way: you create a list of "buddies" or "friends" who also use the same service. The main IM window will display a list of all your buddies/friends, and whether they're at their computer or not. You can then send messages to them, and they can send messages to you. You can also block users, and prevent any user who's not on your buddy list from sending you messages.

Most services also let you create a "chat room," into which you can invite many friends to chat at once.

A chat in an IM client

Let's start with AIM. Just download the AIM client, and double-click on the file once it's downloaded. This will install AIM. Then launch AIM (on Windows, go to Start > All Programs > AOL Instant Messenger), at which point you'll be prompted to create an account. Once you're done, use the "Buddies" menu to find and add your friends to your Buddy List.

The other services work very similarly. Here are the websites where you can download them:

Web-Based Services

You can also use IM on the web itself. The websites Meebo and eBuddy let you sign up once, enter your IM username and password, then send and receive IM messages right from its website.

Just go to www.meebo.com or www.ebuddy.com and sign up.