This is a linear equation in slope-intercept form. We can see that the slope is -1 and the y-intercept is -3 -- the line passes through (0, -3).
To graph this, we can simply plot the point (0, -3) and draw a line with slope negative 1 (this means that for every unit right, we have to move 1 unit down.
I have attached a picture of the graph.
