This guide is slightly deprecated as V3 of 7TV's browser add-on now supports 7TV, BetterTTV, and FrankerFaceZ emotes out of the box, and has some great quality of life chat features that are currently not found in any other emote add-on. You should consider going to 7TV's website and downloading their browser add-on from there.
7TV, BetterTTV, and FrankerFaceZ, more commonly stylized as 7TV, BTTV, and FFZ, are 3rd party emote services for Twitch chat, which aim to enhance a viewer's chatting experience on Twitch by allowing for more emotes to be used in chat, free of charge. Think of it like Discord emojis.
If you're wondering what those weird phrases people in chat seem to be spamming are, it's probably an emote from one of the above mentioned 3rd party emote servi
