This will explain you how to configure mIRC, which is the most used Client for Windows users trying to get on IRC.
Important note: mIRC gives you a window that says after 30 days the trial is over. Even after these 30 days you can still use mIRC. Every time you start up the program, you will have to wait 3 seconds before you can click on "continue".
Three seconds isn't that long guys = ]

Other available clients are for example:

• ChatZilla
• Miranda
• Trillian

After installation

After installing mIRC, you can run it. You will see the following. Note: the red bar won't be red but blue.

AGAIN: Even after these 30 days you can still use mIRC. Every time you start up the program, you will have to wait 3 seconds before you can click on 'continue'. Three seconds isn't that long guys

Click "Continue" and you will see the next window.
Enter your personal information, the way you can see on the image.

After filled in, you can see a menu on the left.
Its standing on 'Connect" and under that it shows "Servers".
Click on "Servers" and you get a new window. On this window, click on 'Add' and fill in as shown below.

Click on the "Add" on the small window, click on "Ok" on the "bigger" window and you finished configuring.

On the left top you see a light bolding.

Click on it to connect to IRC.

You will immediately see a lot of text popping up, relax and wait till it stops.
You will most likely get some pop-up with "Join your favourite channels". At the bottom of that window you can remove the setting to avoid it next time.

In case it didn't showed you a list of all (public) channels, type: 
    /list

You will see that the server generates a list of all channels, from biggest to smallest.
You can easily double click on a channel to join it.
Please make sure to follow local channel rules. This means in general - speaking the language the channel is based on.