I installed the sticker pack. How do I find them?

The stickers are not accessible from the keyboard.  Rather, you must access the stickers by going to the Messages app, choose an existing conversation, press the button at the bottom that shows an A for "apps," and press the button at the bottom with 4 ovals.

Here are the instructions in more detail:
http://www.idownloadblog.com/2016/09/27/how-to-stickers-messages-iphone-ipad/