Just browse to the desired video on youtube or any other supported website and copy the website url. Sharkload will automatically detect this and adds the video to the download list.
After the file info has been fetched you can adjust further options and download the video with one click.
You can find the options for each download item below it's title after the file info has been fetched. Just choose MP3 as your output format.
Yes you can convert your downloaded videos to MP4 and AVI if you whish to. Support for M4A is planned for the future.