The Magnet is a tool that allows you to place your shapes without unwanted space between them. It will help you position your shapes by creating an attraction or snapping effect when you move a point close to another one or the canvas border.
Enabling the Magnet
This tool can be toggled ON and OFF from the toolbaror with the shortcut [CTRL/Cmd + M].
Magnetizing points together
When the magnet mode is activated, you’ll see that when you drag a shape next to another one, a blue area will appear if two vertices (centers included) are close to each other. Once you release your mouse button, these points will be linked.
This whole process also works when you only move one point and not the whole shape, or when you position a shape that you just dragged from the toolbar.
As you can see, if you move one of these points now, the other one will move with it (even when the Magnet is OFF).
Note: be aware that the the points are actually merged, so if you delete one or its shape, the other will also disappear (except if the shape has less than four points.)
Separating merged points
On the other hand, the shapes always stay independent, so if you move one whole shape, the other one won’t be affected and the link between the vertices will be broken.
Note: the Magnet doesn't have to be ON to separate points.
Snapping points to the canvas or a screen outline
When the Magnet is enabled, you also have the possibility to snap points easily on the 4 sides of the canvas (from HM 2.5) or a screen if View → Show Screens is enabled (from HM 2.7).
Similarly to when you merge points together, you'll see a blue indicator that tells you when to drop your selection so that it is placed precisely. However, in this case it works more like a "snap", i.e. you'll feel a kind of resistance when you drag points close to the outline.