It occurs when using the subjunctive mood in English. For example, "if I were you, I would not do that".

Last evening I was in the hotel = this is right (Last evening I were in the hotel = this is wrong) We were in the hotel last evening. = this is right (NB we usually say 'yesterday evening' rather than 'last e These sentences are about real facts. However, if you are talking about situations which you are imagining (hypothetical situations) you say 'I were..' If I were a millionaire, I'd go to live in California.

"was" must come after "I' in your question , the only exception for that rule is when you express a wish in your statement, for example" if i were rich, i would buy whatever car i want.", " if were Superman, i would end corruption"