In these two lectures we have only discussed natural language understanding. However, you should be aware also of the problems in generating natural language. If you have something you want to express (e.g., eats(john, chocolate)), or some goal you want to achieve (e.g., get fred to close the door), then there are many ways you can achieve that through language:
He eats chocolate.
It's chocolate that John eats.
John eats chocolate.
Chocolate is eaten by John.
Close the door.
It's cold in here.
Can you close the door.
A generation system must be able to choose appropriately from among the different possible constructions, based on knowledge of the context. If a complex text is to be written, it must further know how to make that text coherent.
Anyway, thats enough on natural language. The main points to understand are roughly what happens at each stage of analysis (for language understanding), what the problems are and why, and how to write simple grammars in Prolog's DCG formalism.