in plain and short, to graph an inequality, we first graph its EQUALITY graph, and then we do the shading.
so to graph y > x + 3, we first graph y = x + 3, which is just a line, and then do a true/false check on a point to see which side we shade.
let's hmmm check the point say (0,2), x = 0, y = 2.
y > x + 3
2 > 0 + 3
2 > 3 <--- is that true? is 2 really larger than 3? nope, so is false.
that simply means that the point (0, 2) is on the false area, so that's the area we do NOT shade, so <u>we shade the other side</u>.
y > x + 3, means "y" is greater than or larger than that line, but not equals, larger not equal, meaning the values on the borderline are not included, so the line is a dashed line.
check the picture below.