How to use the area of a rectangle to represent the integral

The video tutorial explains how to evaluate an integral by finding the area under a horizontal line function. It breaks down the process of identifying the shape and calculating the area using multiplication. The example used is a simple horizontal line at y=4, and the integral is evaluated from x=1 to x=3, resulting in an area of 8.

What shape is being referred to when discussing the area?

What is the final calculated area based on the evaluation?