What is the Autofill function?

Go to “Settings” -> “System” -> “Languages & input” -> “Autofill service”.
Having your phone automatically type out your information is pretty useful, and Google’s giving Android 10 the ability to make it work with a wider variety of methods that apps and sites could use to prompt you for your password, and will recognize when you enter the last digits of your credit card number and save them too. Also, when you update a password, Android 10 will be smart enough to update the relevant entry, rather than saving a fresh one and leaving you confused as to which one’s the correct one.