Adding and adjusting connections with the Magnet tool
Use this tool to add magnets to a shape or to edit a shape's existing magnets. 
Magnets are special spots on a shape that attract connection lines. If there are no magnets on a shape, all lines connect to the shape's center. If there is at least one magnet, each connected line is attracted to the nearest one. You can also connect lines directly to magnets, to make sure they stay connected to the same magnet regardless of how the shape is moved. Generally, the magnet position presets in the Connections inspector should be good enough, but sometimes you might want to put magnets in very specific places on a shape.
Even if you haven't turned on Show Magnets in the View menu, an object's magnets become visible when you put the pointer over it with the magnet tool. Click and drag an existing magnet to move it, click a spot with no magnet to create one, or Option-click a magnet to delete it.