The difference of value is what gives the human eye understanding of the dimension?

lines and shapes are a part of the visual elements which can be played with and used to create a mood or feeling in a composition.

some of the other elements include the pattern, color, tone and texture. all these elements serve together as the construction blocks which are used by the artists to create artwork.

lines are used to form drawings and different shapes are formed when these lines are used in certain lengths or angles. so the artist can play with these elements of art to create and express different moods, thus conveying different  meanings.

b.) a 3-d model