On that Freenode site you have two main boxes: one for the channel name and one for the nickname you want to use on that channel.
1. In the "Nickname" box, type what nickname you want to use.
2. In the "Channels" box, type wrongplanet
3. Enter the reCAPTCHA codes as displayed into the area just below their display.
4. Click on the "Connect" button.
That's all you need to do to connect to to the #wrongplanet channel.
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Giraffe: a ruminant with a view.