There are two types of sentences: action, and description.
Action sentences describe an action of the subject, including what is used and who or with what it is used.
Description sentences describe some property of the subject. The property may be a characteristic, a state of existence, or a state of activity.
Usually called auxiliary verbs, keys are special verbs and adjectives. They can only be used in verb and copula phrases; they cannot be used as independent verbs or adjectives. Changing the form of a verb phrase is accomplished by changing the tail of the verb and adding the appropriate key(s).
The verb is a modifier for the key(s). . . . It is incorrect to call the process conjugation. There is no conjugation in Japanese. I choose to call the process formation: forming the verb and keys of a verb phrase.
Every sentence has a subject and a verb or copula.
A sentence does not make sense if it does not have a subject to perform the action or to have some property defined. However, in many exchanges, the speaker/author and listener/reader both know what the subject is, and so the speaker leaves it out.
The topic element is a noun phrase marked by wa or mo. It is unique to the Japanese language. It serves as a preamble to the sentence but must not be considered part of the sentence; it is an introduction only.
An adjective cannot modify another adjective. Since the negative keys are adjectives, the adjective being formed is changed to an adverb by replacing its tail with ku.