If by "share" you are referring to the sharing features of social media
(Facebook, Twitter, etc.) I'm afraid I can't help. I do not participate
in social media, never have, never will. So I have no idea how it's
supposed to work.
Not to mention, I don't use Yosemite, I'm still using Mountain Lion, as
this is the only contemporary Mac unit I own, so I don't need all the
integration and such that comes with Yosemite.
AH!!!!! I think I see what you're saying. I just right clicked on a
file on my desktop. In the pop up menu, I selected "Share", and another
popup up says Message and Air Drop. I don't think either one of these
is meant to mean email. If my guess is correct from a little
experimenting, Message will let you send the file to someone's Yahoo,
Google Talk, etc. instant messenger account. Provided the instant
messenger program is supported. Air Drop apparently lets you send the
file wirelessly to someone near by.
I don't have any way to test what I just wrote, it's all just a guess.