What is the meaning of Be_to?

Used to express an official plan, arrangement, or scheduled event.

Used in the past tense to indicate that something was supposed to happen or was destined to happen.

Used after if to introduce a condition that must be met in order for something to happen or succeed.

Used to give commands, instructions, or to state rules. In negative form, it expresses prohibition.

Used to ask or state what someone should do.

Used to ask how something is possible or achievable

Used after if or in inversion to describe hypothetical or imagined scenarios.

Source: wiktionary.org

See also