Input on viewport view.While out of Play mode

I have been searching for days now and I haven’t been able to find anything to help me use input.

What I am trying to do in my game is to use my mouse input(Left Mouse Button) on the screen to spawn a prefab at the mouses location,

I understand you need to place game objects into the scene while game is not running by a simple click ?
Maybe you’re searching for something like this :

?
I didn’t look at the entire tutorial, but it seems you might find the part you’re missing in this (if i understood your question).