be: general

Be can be an auxiliary verb, used to form progressive and passive structures ( (see here), (see here).

• What are you doing?
• We weren’t told about the meeting.

As an auxiliary verb, be can have progressive forms in passive structures (see here).

• The hospital is being rebuilt.
• I knew we were being watched.

Be can also be a linking verb, used to join a subject to a complement.

• This is difficult.
• Andy was very tired.

Progressive forms of the linking verb be are not usual.

• It’s cold today. (not It’s being cold today.)

But they are possible in some cases (see here).

• You’re being stupid.

Questions and negatives are formed without do, but do is used in negative and emphatic imperatives (see here).

• Don’t be afraid.
• Do be careful. (stronger than Be careful.)

note

For the structure there is, used to introduce indefinite subjects, (see here).

For be + infinitive (e.g. She is to arrive tomorrow), (see here).

For contractions (e.g. I’m, isn’t), (see here).