Essential means very basic or necessary. A good frying pan is one of a short list of kitchen essentials every cook must have. To prevent fires, it's essential to turn off appliances before leaving the house.
The adjective essential is often followed by to or that: It is essential to wash your hands. It is essential that you dry them after. This adjective is from Middle English essencial, from Late Latin essentialis, from Latin essentia "the basic nature of a thing, its essence" plus the Latin suffix -alis "relating to."