These words "<em>are, is, am, is</em>" are known as direct or main verbs of a sentence. Thus they act as the doing words or the main action words in the sentences. Without them the sentences may be meaningless or incomplete.
In 1 above, <u><em>are</em></u> functions as a <em>Linking Verb</em>. The phrase a good student is a state of being and provides additional information (in third person singular) about the subject "You".
The same explanation goes for <u><em>is</em></u> and <u><em>am</em></u>.
Please note: Any word which in a sentence, that is used to connect a subject to an additional information about the subject is called a <u>Linking Verb</u>.
In "Star Food," Dade works in his father's grocery store, Star Food. When a middle-aged woman starts shoplifting, he must figure out what he wants to do with his life and what kind of person he wants to be. In the end, he allows the shoplifter to go free.