To zoom in the viewing area, select the Zoom tool. Click and hold your mouse button down on the viewing area, then move your mouse up to zoom in or down to zoom out. (Shortcut key Z)
You can also scroll your mouse wheel to zoom in and out (when the mouse cursor is within the viewing area). This method provides a convenient temporary zoom while keeping the current tool active (such as the Edit tool).
Note: When you zoom in, the scene is centered on the location of your mouse pointer.
Tip: this tool is also available in the Navigation menu and Context menu > Navigation.