Do someone has any ideas of how to achieve this kind of behavior ?
See it in animated gif :

- The user can drag a box using the mouse and when a collision occur, the box stop moving and snap to the other box.

https://i.ibb.co/m5Z1yK6/test.gif

Is there any links to the theory used for this kind of behavior ?

(I want to achieve this using Unity but any kind of sample / source is ok).

What do you have so far?

Everything you need to do this (beyond basic motion of the box) should be available in the Collider and Collision documentation.