On the main page swipe down (or up) to see all available Emojis. Then press on the emoji you wish to use:
When pressed, the emoji will be automatically copied to your clipboard:
Now go to your email or instant messaging app.
For example on imessage, press in the input field until “paste” dialogue appears, and press “paste”:
Once done, you can send the emoji like you would any text:
On Facebook Instant Messenger, in similar manner, press the input field until the “paste” dialogue appears:
And press “paste” the Emoji will appear, you can now press Send Photo or Edit before sending: