The azimuth is the direction the solar panels face to maximize their exposure to the sun. On a typical residential home with a sloped roof, the azimuth of the solar panels faces the same direction as the roof slope and is aligned to the lower eave of the roof.
On a commercial rooftop system, the azimuth of the solar panels are typically aligned with the south or west facing edge of the roof (in the Northern Hemisphere).
PVSketch has a simple button that "snaps" the azimuth to the lower roof edge of your choice. This video explains how to click the Snap button and then use the pointer to highlight and select the roof edge for the desired roof edge.