Except so many of them are culturally specific, like the horn emoji on the front page has roots in postal systems (both in Japan and Europe). This page doesn't tell you that. Even this random website does a better job of giving context:
http://emojipedia.org/postal-horn/
Well, Emoji are originally Japanese so you always have to keep that in mind.
The point is "what is this emoji?" Knowing emoji started in Japan still doesn't tell you what the emoji is or means!