There is really not much to say about this mod! But for a mod like this, that's a good thing, right?

Emojis does exactly what it says on the tin: it allows you to type Unicode emojis in chat easily using the colon (':') shortcuts, similar to how messengers like Signal, Element, Teams or Discord work. The names are the ones you are familiar with (e. g. :pensive:). Since the mod just inserts a standard Unicode emoji character, everyone can see the emojis you send, whether they have the mod installed or not.

By the way, if you don't like the standard, black-and-white fallback style of the emojis, that's because Minecraft's default font does not include colourful and fancy emojis. I recommend using resource packs that add an emoji-capable font! I personally use one called "Cheerful", which adds little pixel-art emoji that fit very well with the Minecraft style.