To start a fire with flint & steel you will need a steel striker, a piece of flint, some charcloth or charwood, and tinder such as jute or hemp.

Pull tinder apart and form a nest out of it.

Find a sharp edge on the flint and hold the charwood on it.

Using the flat "striking" side of the steel strike along the sharp edge of the flint until the charwood catches a spark.

Put burning charwood in tinder nest and fold nest around the charwood then blow into it until it bursts into flame. Immediately place burning nest into the campfire or grill that you are starting.