Canvas is the place where you can construct/import/edit your molecules. There are several options to help you to see always the structure that is in your focus of interest.
Navigating on the canvas
You can navigate on the canvas using the vertical and horizontal scrollbar.
Regardless of the currently active tool, you can get into "navigation mode" by pushing down the middle mouse button as well.
Modifying the zoom ratio
The contents of the canvas can be reduced or magnified at will with the Zoom In/ Zoom Out buttons on the General toolbar. The zoom ratio can be changed by zooming with the mouse wheel is centered at the cursor position. (With this function, you can virtually "move" the canvas.)
The Zoom All button on the General toolbar sets the optimal magnification to view everything on the canvas. The "Enter" shortcut can also be used for this purpose.
The Zoom to Selection button on the same toolbar (or the "Ctrl + Enter" (link to shortcuts proper place) keyboard shortcut) increases the zoom ratio placing the selected object in the center.