Auto alignment (Alt+K)
SMM uses third-party software or its own internal code to find corresponding (homologous) points in a series of movie source frames.
The feature-detection method that SMM uses has significant advantages over the older pixel-pattern 2D correlation methods.
The features are invariant to translation and rotation, and to some extent to vergence and brightness.
Using the knowledge of those hundreds or few thousand points, SMM applies translation, simple rotation, scaling, perspective-rotation and color-equalisation to correct the images.
You may pick a single pair of frames from the movies and apply the same corrections to all frames or you may individually correct every pair of frames.
Set all your correction preferences in Auto alignment settings.