Why The Smith chart is a graphical map of the complex reflection coefficient overlaid with normalized resistance and reactance circles, so moving along a transmission line is just rotating around the chart center. That makes it ideal for stub matching: you rotate from the load toward the generator until you land on the unity-resistance circle, which fixes the stub's position, then read the reactance you must cancel to get the stub's length. Working these problems graphically is the classic textbook use of the chart.
Watch out Finding a line's characteristic impedance from conductor diameter and spacing, or its loss per 100 feet from materials and velocity factor, comes from formulas or manufacturer data tables, not from the chart, and antenna gain is not a transmission line impedance problem at all.
Smith chart = impedance along a line. Rotate toward the generator, add a stub. Anything about physical dimensions or loss is not it.