Houdini Basic Viewport Controls

ALT + Left mouse + Drag = Tumble the camera in the viewport 

ALT + Middle mouse + Drag = Pan/Track the camera 

ALT + Right mouse + Drag = Zoom the camera 

SPACE + H = Frame the camera to all objects in the scene 

SPACE + Z = Frame the camera on any object that the cursor is over 

SPACE + G = Frame the camera on the selected object 

SPACE + B = Show perspective views (Top, Front, Right + Perspective) 

Hovering over one of the views and pressing SPACE + B again will expand that view