Drag and drop/ GRID mechanics

Hi there, I did a game setup following this example Blueprint Actor Setup | Unreal Engine Documentation
And I made a aimple grid like this:

I have some questions now: How do I drag the box I did following the tutorial, to snap on specific locations of this grid?
How do I make another box, snap to Z when coliding with other boxes already on my grid?

Any link with related question or tutorial will be of great help. Thanks