The left button is used for selection and stylization of the scene. This specific behavior depends upon the current mode.
Object attributes can now be edited.
The lines you draw affect stylization.
In all modes, the right mouse button is used for camera manipulation.
Translation parallel to image plane.
Translation perpendicular to image plane ("zooming").
Define a center of rotation (blue sphere) and use it.
Define a point on the model surface and position it at the center of the window.