All shapes drawn to the screen have a position that is specified as a coordinate. All coordinates are measured as the distance from the origin in units of pixels. The origin [0, 0] is the coordinate is in the upper left of the window and the coordinate in the lower right is [width-1, height-1].
# Sets the screen to be 640 pixels wide and 360 pixels high
size(640, 360)
# Set the background to black and turn off the fill color
background(0)
noFill()
# The two parameters of the point() method each specify coordinates.
# The first parameter is the x-coordinate and the second is the Y
stroke(255)
point(width * 0.5, height * 0.5)
point(width * 0.5, height * 0.25)
# Coordinates are used for drawing all shapes, not just points.
# Parameters for different functions are used for different purposes.
# For example, the first two parameters to line() specify
# the coordinates of the first endpoint and the second two parameters
# specify the second endpoint
stroke(0, 153, 255)
line(0, height * 0.33, width, height * 0.33)
# By default, the first two parameters to rect() are the
# coordinates of the upper-left corner and the second pair
# is the width and height
stroke(255, 153, 0)
rect(width * 0.25, height * 0.1, width * 0.5, height * 0.8)