Question

When we are determining the value of an integral using a graph, which numbers do we add?

Answer 1

you want to add up all of the sums of the approximating rectangles as their width, dx, approaches 0. You could add a lot of approximate triangles, but it's better just to take the antiderivative of the general rectangle area formula as an integral.
for example, if you have a function, f(x), and it's above the x axis, then it's general height is f(x) - 0. now the width is delta x. when you take the integral, it turns to a "dx." your bounds of integration are how far on the line via x coordinates you would like to measure.

Answer 2

If you give me an example, I can help