Emojis are just special characters that look like pictures instead of letters and numbers. They are normally governed by the phone's OS.
The various phone makers agree to add new ones every now and then. While Apple tends to add them very quickly, Android phones tend to get new ones only during OS upgrades. Until you get updated, there is nothing you can do.
Some apps do a bit more control over this. Thus, when using those apps, you may see the new emojis in that app but not anywhere else.