Oh, you have to click on "+ Add Media" in the lower left corner of the comment box. Then enter the name of the emoticon you want to add to the comment. 
But I'm using the app. Anyway to do that by text?
I don't like the app and don't know how it works now. I only used it once and really disliked it. So I'm only using the website now.
And I dunno how to do by text
And I dunno how to do by text