Be as an auxiliary verb..

With the Present Participles

Be is used with the present participles of verbs to make the present and past progressive tenses.

·         I am writing. (Present Progressive) 

·         She was standing at the gate. (Past Progressive) 

·         She is knitting a sweater. (Present Progressive) 

·         You were sleeping. (Past progressive) 

With the Past Participles of Transitive verbs

Be can combine with the past participles of transitive verbs to form the passive voice.

·         I was shocked. 

·         He was treated badly. 

·         You are rewarded for your service. 

·         They are sold cheap. 

With the past participles of Intransitive verbs

Be can combine with the past participles of certain intransitive verbs to form the perfect tense.

·         He is gone. (= He has gone.) 

·         You are quite grown up. (=You have quite grown up.)