Toxygen support smileys. Smiley is small picture which replaces some symbol or combination of symbols. If you want to create your own smiley pack, create directory in src/smileys/. This directory must contain images with smileys and config.json. Example of config.json:
{":)": "one.png", ":(": "two.png"}
Animated smileys (.gif) are supported too.
Sticker is inline image. If you want to create your own sticker pack, create directory in src/stickers/ and place your stickers there.
Users can import smileys and stickers using menu: Settings -> Interface