Mirc:

This chat program is one of the most popular as you can reach the most people from this one

It works simple enough, you choose a nickname (one that does not show your sex is best..) and then connect to one of the servers, each server has a list of channels, you choose which one to join( depending on the subject of the channel),
A new window will pop up with a list of people on that channel and you can choose whith who to chat with

+ many servers and many users
+ You can be very easily anonimous
- Sometimes people can be rude
- not able to send messages when one of your buddies is ofline

tips:
-Don,t use caps lock to much, it is translated as shouting
-never give your personal info to easy, get to know the persons you chat with for some time.(this rule is for all chat programs!)

ICQ:

Easier then mirc but only one server to use

After installing the program you have to register for free first.
Then you open icq and find people of same interests or location with their white pages search engine.
You then add them to your buddies list
and of you go chatting...
You are also able to send messages when the other user is of-line!

+ able to send msg ofline
+ able to save all chats and msg,s
+ You can now also send sms messages to your friends from icq
- only one server

Odigo:

This one is a lot like Icq only it has some extra,s.

While you surf the web you can see which
odigo users are on the same site as you and
chat with them

Also you can leave notes on certain sites you
visit for others to read
Need to register here for free first too
- It doea slow down your surfing a bit.

ChatPoint:

Here you chat in chatrooms with a cartoon representing you,
Need to have Java enabled!

Furcadia

Now this one is different, here you can chat and see too.

You choose a avatar (a figure that is suppossed to be you) and enter the virtual world of Furcadia!
Must register for free first and download the program.

Others:

There are many other chat programs available, some more are:

This is the AOL instant messenger, just go to aol.com to download

This one is from Msn.com (also offers Hotmail)

This one is from Yahoo.com