Here are some synonyms for "necessary":
* Essential
* Indispensable
* Vital
* Crucial
* Imperative
* Requisite
* Required
Here are some examples of how "necessary" is used:
* "It is necessary to have a passport to travel internationally." This means that a passport is essential for international travel, and you cannot travel without one.
* "A good night's sleep is necessary for optimal health." This means that sleep is important for health, and you cannot be healthy without it.
* "The team's success was necessary for the company to grow." This means that the team's success was crucial for the company's growth, and the company would not have grown without it.
In short, "necessary" refers to something that is essential for a desired result or outcome, making it absolutely crucial and impossible to do without.