my snapping snap to the inside of the inside how can i make it snap to the outsode like in the vid
If your snapping is set to vertex snapping like in the video, hover your mouse pointer over a vertex that is on the outside of the planks. It should snap to that vertex.
If, in side view, you start to the left of that vertex, it will snap, but stay on the left side. And vice versa:
(abit of a late reply, but perhaps this will help someone else)
You can change snapping to face, that way you can move it along the Y axis and have it snap directly to the face even without a vertex located there.
Also it often matters which way the object is approaching the snapping point. If you are moving it from the inside it will snap to the inside. Likewise if you are moving it towards the planks from outside it will snap to the outside.