It can be used in many contexts, but here are some common ones:
* Essential for something: "L'eau est essentiel à la vie." (Water is essential for life).
* Something that is absolutely necessary: "C'est un élément essentiel de la réussite." (This is an essential element of success).
* Of great importance: "Le respect est essentiel dans toute relation." (Respect is essential in any relationship).
In some cases, "essentiel" might be used as a noun, meaning "essentials" in English. For example:
* "J'ai apporté l'essentiel pour le voyage." (I brought the essentials for the trip).
Do you have a specific context in mind? If you can tell me what sentence or situation you encountered the word in, I can give you a more precise explanation.