There are a couple of ways to zoom in to the very details of your diagram.
The most obvious way is to use the various View | Zoom menu commands. There are even a few keyboard shortcuts available to zoom in (⇧+⌥+⌘+=) and zoom out (⇧+⌥+⌘+-) in 100% steps increments. Unless you are using an American keyboard layout, none of these two keyboard shortcuts will be very intuitive to you.
A more intuitive keyboard shortcut is ⌥+⌘+0, which will bring the canvas back to the actual size of your diagram.
The second way is to use the Zoom button( ) at the bottom of your canvas. You can use the Zoom button to zoom to a certain percentage—this ...