A verb is the active part of the sentence, and tells what is being done or what characteristic is observed.
A noun is a name word, and may be the subject of a sentence, the object of a verb, or the object of a preposition.
An adjective is a describing word, that tells something about a noun or pronoun; either identifying it or something.
---
You can define each of the words in a sentence by its part of speech, and by the role it plays in the sentence.
The boy kicked the red ball quickly.
[the boy - complete subject]
[kicked the red ball quickly - complete predicate]
the - article (determiner)
boy - noun - simple subject
kicked - verb - simple predicate
the - article
red - adjective, modifies ball
ball - noun - direct object
quickly - adverb, modifies hit
a. verb : kicked
b. noun: boy, ball
c. adjective: red