Examples of usage:

Be

I will be there tomorrow.

(use "be" after modals)

I might be late.

He wants to be an astronaut.

(use "be" with "to" in the infinitive)

"To be or not to be;" that is the question.

Be nice now.

(use "be" in the imperative)

Please be quiet.

Is / Am / Are

Bill is sick today.

(use "is" with he/she/it in the present tense)

She is a doctor.

It is not time yet.

She is not here right now.

(use 's as the contracted form of "is")

She isn't here right now.

She's not here right now.

Mr. Lee is eating dinner right now.

(use "is" with he/she/it in the present continuous)

She's talking on the phone.

Maggie's leaving tomorrow.

The dog is running down the street.

(use "is" with he/she/it in the present continuous)

I am a lawyer.

(use "am" with I in the present tense)

I am not a liar.

I'm happy to be here.

(use 'm as the contracted form of "am")

I'm not going anywhere.

We are at the office.

(Use "are" with they/we/you in the present tense.)

Jack and Jill are over the hill.

You are welcome anytime.

They're in the building.

(Use 're as the contracted form of "are")

We're on the way.

You're kidding!

We are working hard.
(Use "are" with you/we/they in the pres. continuous.)

They are hardly working.

The boys are waiting to see her.

We are not paying for the extra drink.

(The negative "are not" can be contracted two ways)

We're not paying for the extra drink.

We aren't paying for the extra drink.

Was / Were

I was here yesterday, so was Tina.

(Use "was" with I/ he/she and it in the past tense.)

It was a really nice trip.

Henry was at the dentist's for two hours.

We were in Spain last week.

(Use "were" with you/we/they in the past tense.)

The Smiths were on vacation.

You were the only one here.

They weren't at work yesterday.

(The only contracted forms are wasn't/weren't.)

Jared wasn't here either.

I wasn't aware of that.

Been

Rachel has been there before.

(Use "been" after have/has/had.)

I've never been to Maine.

We have been living here since June.

You should have been paying attention.

Being

Being a good sport is important.

(Use "being" when a gerund form of be is required.)

Being on time is essential.

I was being a jerk.

(Use "being" when "be" is used in the continuous.)