The basic function of was / were at four situations :
a) I / He / She was in high school last here. ( Simple Past, Independent use as main verb)
We/ You / They were at canteen yesterday at 9 am. ( ,, ,, ,, )
b) He was drawing a picture. ( Past Continuous , helping ‘ing form’)
We were playing cricket last Sunday. ( ,, ,, ,, )
c) She was invited to the party. ( Simple past , Passive voice, helping V3)
We were served a delicious salad at the party . ( ,, ,, ,, )
d) He was being observed by the teacher. (Past Continuous, P.V,helps ‘being’+ V3)
They were being given certificates by the Principal. ( ,, ,, ,, )
The basic uses of ‘be, been , being’ : These are secondary ‘be-forms’. They can’t start a verb form. They follow other helping verbs and help another main verb.
Be : a) It will be nice. / He may be there in an hour. ( ‘be’ follows a modal auxiliary )
b) It will be corrected. ( It follows a modal verb and helps V3 . Passive voice, Simple Future Tense / Simple Present with ‘can, may’..etc. )
c) I shall be studying B.Tech. next year. (It follows a modal verb and helps ‘ing form’. Future Continuous Tense / Present continuous Tense with ‘can, may’..etc) .
Been : a) I have been practicing dance since my childhood. / She had been studying Diploma. / They will have been pursuing B.Tech. ( ‘been’ follows have form and helps ‘ing form’, Present / Past / Future Perfect Continuous Tense )
b) This parcel has been received just now. / The guests have been received . / We shall have been informed. (been’ follows have form and helps V3 form, Passive Voice , Present / Past / Future Perfect Tense )
c) I have been to this city several times.( I visited many times )
The book had been there on the table . ( It was there when I saw it )
Being : a) The weather being rainy, the match was cancelled.
b) This book is being sold worldwide. ( ‘being’ follows another primary ‘be form’ and helps V3, Passive voice. Present/ Past Continuous Tense )
( The given examples are the basic functions of ‘be forms’ in commonly used situations. There may be other rare situations where we can use them. Please go back to the Tenses Tables of Active& Passive voice and observe the function of 'be forms')