Ok, thank you MattP.
About those tutorials... I have watched them before my post here. But it seems like mouse-over for make object snapping candidate doesn't work all the time. Not sure why it happens. Bug maybe?
There are those all snapping options... For snapping I just need something very simple working like this function in Google Drawings. Is there a way to achieve this? In your tutorial with simple objects it seems it should work this way but I'm wondering why I cannot reproduce that in my project, even when I have same snapping settings turned on. :(