Navigating the rules of the English language can often be tricky. The incorrect usage of common verbs is common among native speakers, and the confusion between common verbs creates difficulty for non-native speakers. When using do and does and is, am and are, speakers need to know the differences between the two verb forms.
Do and does come from the infinitive "to do." Is, am and are, on the other hand, come from the infinitive "to be."
The "to do" verbs denote actions. The subject is physically taking action. The "to be" verb denotes existence.
"To do" is used as either a main verb, where it stands alone as the action verb, or an auxiliary verb, where it is paired with a main verb in an interrogatory statement. For example, "to do" used as a main verb could read, "The students do their homework." If used as an auxiliary verb, a sentence may say, "Do you always take the bus?" The "to be" verb has more versatility. It is used as a stative verb, which tells the status of a subject. For example, "I am tired." It is used as a linking verb, where it helps another verb. For example, "I am working on my homework." "To be" is also used to ask simple yes and no questions. For example, "Are you listening?"
Do and does are used in the active voice. For example, "They do the right thing." Is, am and are can be used with either the active voice or the passive voice. The subject makes an existence claim when using is, am and are in the active voice. For example, "I am here." When used passively, the action affects the subject. For example, "Languages are spoken."