First step is to graph the equality
y=x-3
In a graph of y=mx+b
m is the slope, and in this case, m=1, which means that y increases by one for each step in x=1. This creates a line at 45 degrees from bottom left to top right, passing through the origin.
The b=-3 means the line has to be lowered from the origin by 3 units.
b is called the y-intercept, where the line cuts the y-axis (=-3).
So with the line drawn, we need to know the style of the line.
If the inequality is a strict inequality (< or >), then the line is drawn dotted.
If the line is an inequality together with an equality ( ≤ or ≥ or = ), then it is drawn solid.
Finally, an inequality has to be shaded on the side where the inequality is true.
Looking at the inequality, y<x-3 we can read immediately that the valid side is where y is small ("y is less"), so we shade the part below the line.
The finished graph is attached.