Student or Learner
what is the appropriate usage of be?
"To be" is a verb that has different forms in the present, past and future tenses.
In the present: I am ...; He is... ; They are...
In the past: I was...; We were...
In the future: I will be... ("be" has to be accompanied by a model verb)
"to be" can be used as an infinitive, for example: "I want to be a doctor"
Also, it can be used in another form, like: "He knows everything, be it math, chemistry or English"
Your question is generic, I tried to cover all aspects of "to be".