I dunno what the right way is but I type a : and then that pops up a like search thing that lets you pick one. Once you pick one it pops this big long string of bullshit into your post that becomes an emoji. So for example if you type :sicko you get a bunch of stuff like
@ComradeLuz@hexbear.net additionally to what infamousbIt said; when you are typing up a new comment or reply, one of the buttons above the text field looks like a smiley face (between "link" and "upload image.") You can click this to open up the emoji picker menu. The asterisk tab on the far right of this window is where you can find all of the custom emojis we have.