Who helps me with this block of logic?

I'm still learning Stencyl and your advice will make me better understand the logic of programming with this program.
I'm making a small children's puzzle game with drag&drop. There is a square that has to be moved on top of another square. If the two collide, then the second square is positioned above the first square, otherwise the square returns to its original position.
I was able to make the whole thing work, but I would like the condition "when the two collide" to happen only when the mouse is released. In fact, it happens that if you move the square at random, they are "attracted" without the player's control and this is not good.
The child must understand that ONLY when the corect square is above on the other and, he releasing the mouse, the two dowels attract and not before.
I've been working on it for three days without being able to solve it.

That should be the logic:
1) Click on the first block and drag it with the mouse.
2) If the first block collides with the second and the user releases the mouse then the position of the first and second block are identical (therefore the second one goes over the first one) - would it be useful if there were an instruction like "the first actor is above the second actor"? (but there is no such education)
...
Suggestions?

I've seen a similar thread posted previously. If I find it, I'll let you know.

There are blocks under ACTORS > DRAW > LAYER that lets you get an actors position (z-index) on  a layer.

If you are using fixed positions for the targets, you  can use the x and y coordinates to check where the actor is dropped, and if this corresponds with a targets coordinates (+ -  a suitable number, or it gets too precise) you can proceed with your check for correct answer.  There is no need for collision checks.