First thing you need to do is download 1-Click YouTube To MP3 Converter
Be careful while installing so you don't get dragged into a toolbar or any other special offer
Locate on Youtube something you want to download and copy the URL
Then paste it as shown below
Next choose how you want it saved. You can keep the file as whole or just the audio. I'm saving this as an MP3
You can keep the FLV file (raw and uncoverted) or check the box to remove it. Then choose where you want it saved and click the get/convert button
It will then save it to your designated area, but not like this. It'll actually save it as some weird file name that you'll have to rename.
You're done