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A fun way to learn about emojis is in this post:
I showed my emotions to a model and aspiring actress and…- 向个有志愿成为演员的模特儿表露情感。。。 (by @ace108)
It applies to both using emojis in post as well as comments.
Hope that helps.

I would suggest you visit @blueorgy's post 👍 😎 👀 💃 Steemit Emojis Master List 2 🚀 😝 🌍 🍒 for detailed information on using emoji's.