It has an official list of what they actually represent (which is what is read out when using text to voice software) and shows you what they actually look like on different platforms. You can paste an emoji into the search bar to look up what it means. Very handy if you are like me and spend way too much time wondering if that little face is actually smiling or grimacing.
I realised yesterday when the blackbird in my name showed as a red bird and a black square on my PC just how different they can display too. And all the little faces are so small, there are quite a few I can't tell what they are supposed to be.