-- On your graph, make a dot at the origin. That's the point (0, 0).
-- Make another dot at any one of these points:
(1,4), or (2,8), or (3,12), or (4,16) .
It's your choice
-- Put your ruler down on the paper, with the straight edge
against both points.
-- Using your pencil, draw a straight line along the edge of the ruler.
You can go as far as you want in each direction. Technically, the
line has no ends, and keeps going forever in both directions.
-- The line you drew is the graph of y = 4x .