Variables are used for storing values. In this example, change the values of variables to affect the composition.

size(640, 360)
background(0)
stroke(153)
strokeWeight(4)
strokeCap(SQUARE)

a = 50
b = 120
c = 180

line(a, b, a + c, b)
line(a, b + 10, a + c, b + 10)
line(a, b + 20, a + c, b + 20)
line(a, b + 30, a + c, b + 30)

a = a + c
b = height - b

line(a, b, a + c, b)
line(a, b + 10, a + c, b + 10)
line(a, b + 20, a + c, b + 20)
line(a, b + 30, a + c, b + 30)

a = a + c
b = height - b

line(a, b, a + c, b)
line(a, b + 10, a + c, b + 10)
line(a, b + 20, a + c, b + 20)
line(a, b + 30, a + c, b + 30)