Aside from using default emotes, you can also upload your custom ones. To do so, go to the Subscriptions page and navigate to the Emotes tab. Then, scroll down to Collections and select Add Emote. This will display a panel on the right, so make sure to click on Select from Gallery.
Once in the gallery, select Upload File to start uploading your custom emotes!
Custom emotes are currently limited to 5 and collections are limited to 1.