An ellipse is a closed curve with two focal points. Kepler found that planetary motion was better described by ellipses than by perfect circles, with the Sun at one focus. In this model, the planet’s distance from the Sun changes along its path.
A circle is a special case of an ellipse, so an elliptical orbit can still look nearly circular. Textbook diagrams often exaggerate the elongation to make the geometry visible. The useful feature to notice is where the Sun sits, not merely how stretched the drawing looks.