Cross hatching is the method of using black and white lines to give the illusion of tone or shade in a black and white drawing , which by definition, has only two tones or shade – Black and white
Hatching is filling in an area with parallel lines to create an illusion of tone or shade.
Adding another layer of lines, drawn in a different direction, gives the illusion of a darker shade.
Adding more layers in different directions, darkens the filled area more with each layer.
Used simply it is a way of filling areas with tone or shade.
Used creatively, cross hatching can also give the illusion or impression of depth or 3Dness.
It requires fine motor skills, patience and persistence to learn to draw lines at equal distances and make the tonal vale look even.
Practice a little bit everyday and you will soon be a master of Coss hatching.