I could tell you the *usual* features. Why do teachers/authors love to pick words like "essential"?
A computer language usually has variables that reference the computer memory or registers and has syntax for causing arithmetic and logical operations to be performed on those locations.
It has constructs for controlling the flow of a program. It will usually have ways to do input and output, although, you can think of these as just setting or retrieving data from memory locations.
Perhaps your textbook has a specific list of the features and your teacher expects you to reproduce that list.
I like Eddie's answer. Very good.
I would say an essential feature of a computer language: it has to be readable to a human. There has to be a way of converting the human-readable language into code the computer can process.
You explain it first.
