#### Answer

Refer to the image below for the sketch.

#### Work Step by Step

RECALL:
The point $(x, y)$ has:
$x$ = directed distance of the point from the y-axis (negative when to the left of the y-axis, positive when to the right)
$y$ = directed distance of the point from the x-axis (negative when below the x-axis, positive when above)
Thus. the set $\left\{(x, y)|y\lt 3\right\}$ represents the set of points whose y-values less than 3. These points are found in the region below the horizontal line is $y=3$.
Since the points on the line $y=3$ are not included, the line will be graphed using broken lines.
(refer to the attached image in the answer part)