"Be" verb indicate a state of being. The rules associated with "Be" verb are as follows
1. Verbs must match subjects.
Example : I am a doctor. / He is sleepy.
2. Negative sentences need ‘not' after the verb.Example : I am not a doctor. / He is not sleepy.
3. The verb comes first in interrogative sentences. Example : Am I a doctor? / Is he sleepy?
4. "Are not" (is not) can be shortened to "aren't" (isn't). Example : He isn't sleepy./ We aren't there.