Ha; it was still up in another tab from last time. And it’s bookmarked now.
Welcome to BA, @Ahmed_Hamada 
The following post was written for episode 4, before the Shrinkwrap Modifier, but it examines why things clip and how the new snapping works, and that’s really what you need to know (Andrew didn’t get into any details, but I find that knowing why things work the way they do really helps down the line). Object clipping into each others - #14 by piranha4D