y=mx+b is the slope intercept equation
m is the slope and b is the y-intercept, or where the line crosses the y axis.
this will always be a straight line and in your case, it's a negative slope that goes from the top left to bottom right.
i always start on the y-intercept, so plot a point at (0,1)
-2 actually means -2/1 and with rise over run that means 2 down, one across
to summarized, start at (0,1) go down two, one across, plot a point and connect the two which goes on forever.