Pathetic.. but how do you send a challenge?

Ok I'm probably missing something huge here but when I click "challenge a friend" or whatever after a song is over it takes me to my email so I can send an email saying "I got xxx,xxx on xxxxxxxxx" but I just want it to send the challenge like in the news menu from the home-page (I guess you could call it) of the app itself. Do those the same thing? If so how do you get a person's email?

Or is there a different way to do it? I'm so lost.
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