Basically, there are two components of Natural Language Processing systems:
a. Natural Language Understanding (NLU)

In this, we have to understand the basic tasks −

Basically, the mapping to given input in natural language into useful representations.
Analyzing different aspects of the language.
b. Natural Language Generation (NLG)

We have to produce meaningful phrases and sentences. That is in the form of natural language from internal representation.

As this process involves:

a. Text planning
In this process, we have to retrieve the relevant content from a knowledge base.

b. Sentence planning
We have to choose required words for setting a tone of the sentence.

c. Text Realization
Basically, it’s process of mapping sentence plan into sentence structure.
Although, the NLU is harder than NLG