Sandbox Ghost Merge Canvas

I know how to Ghost Merge Regular,but i don't get how to do it with the map.
Can you show like a tutorial on it because i don't get it..

GT:Str8ezy

 

On Ghost Merge Canvases, you have to start a new round first, after that dummie one object of your choice, place it and ghost merge it.
It works like regular Ghost Merging, but you only have to dummie one object.

 

I'm being a noob what's (Dummy a object) mean??

 

just spawning the object as a spartan and making it feel like a "movable" object falling from a distance, and that's why the first object disappears in 30 sec doing a normal ghostmerging. But in this case, you just drop it as a spartan and grab it and set it