If the streamer doesn’t yet have any subscribers, he/she is only allowed to upload one emoticon as an affiliate. For each further one you already need subscriber points. You will receive subscriber points with subscriptions.
Here you can find all other guidelines and details about Twitch Subscriber Emoticons:
On your Twitch Dashboard you will find the menu item “Emoticons” in “Settings”. If you click on “Edit” you can upload your Twitch Emotes as PNG. In the same menu you will also find options to change or delete already existing emoticons. When uploading the emoticon you can assign a code with up to 20 digits to activate the Twitch Emote. This code may contain the characters A-Z and the digits 0-9.
Twitch emotes must be uploaded as PNG and should have a transparent background. They are available in three different sizes, for each of which a single PNG file must be uploaded: 28 x 28, 56 x 56 and 112 x 112. The individual files shouldn’t be larger than 25 kb. A detailed guide with more information can be found here on Twitch.