Question

What is "verb to be" and how and where we can use it?

Answer 1

You have already used the verb "to be" in your question, when you used the conjugated verb "is". Other conjugations of "to be" in English are: was, am, were are, and being. "To be" is called the infinitive (unconjugated) form of the verb. (I never learned this until I studied foreign languages!)

Answer 2

For more about the conjugations of "to be", see

http://www.scientificpsychic.com/grammar/to_be.html

The form that you use depends upon the subject pronoun and the tense (past, present, progressive, past participle or subjunctive). The table at the website above explains it better. The future tense of "to be" is just "will be".