The verb "to be" is a special verb that uses unique forms for its conjugation.
Here are the forms of the verb "to be" in Present Indicative Active.
Reminder: The ν in brackets is a movable ν. It often appears before words starting with vowels or at the end of a sentence or a clause. But it can be omitted as well.
Here are the forms of the Future Indicative Active:
Here are the forms of the Imperfect Indicative Active. It is the only past tense of εἰμί, and so can be translated with was or were.
The Present Infinitive Active form of this verb is -- εἶναι.
The Future Infinitive Active form is -- ἔσεσθαι.