What are Animoji?
Animoji stands for animated emoji. This means you can now scan and record your expressions onto an emoji. You can talk, smile, laugh, frown, shake your head or make any other facial expressions and the animoji will do the same. In iOS 12 Beta, Apple has added tongue detection! You can finally stick your tongue out at all those people who deserve it ha-ha.
How do I use Animoji?
Animoji can be accessed through iMessage. 
Open iMessage and then select the Animoji iMessage App. 
Then select which character you would like to use, hit the record button, make funny faces and talk, stop recording and send it! It’s that simple.
Only iPhone X and later models support animoji.
What are Memoji?
A memoji is nothing but an animoji of yourself! So, you now have the option of customising an animoji. Everything from skin colour, eyes, nose, lips and many more can be customised. Everything else works the same way as animoji.
That’s me on the left!
To create a memoji,
Go to iMessage
Go to the Animoji iMessage App
Select the “+” sign 
Start selecting features to create a memoji that looks like you or let your imagination run wild and create an alter ego memoji! Select Done to save the memoji.
The memoji will now appear in the list of animoji.
Very interesting. Why can’t we have the privilege of this feature in an iPhone 7 or 8?
Only the iPhone X has the true depth sensors in the front which can accurately create a 3D map of your face. Since all iPhones before the iPhone X don’t have those sensors, Animoji will only work on the iPhone X and later models.