Let's take a simple example of dragging a button around.
Suppose you have two types of container controls:
1) an X-Y layout
2) a flow layout (assume left to right)
When you click to drag the button, record the x-offset and y-offset from the click to the top left corner of the control. As well, record the index of the control within the Controls collection.
As the mouse moves, first check if the mouse has changed container controls.
If so, then remove the button from its current parent and add it to the new parent.
If the button is added to a flow control, then you need to calculate the new index. To do this, calculate the distance from the mouse to the closest edge of a bounding box of all other controls. Then if the mouse is left of the center of that control, insert to that control's index minus 1, otherwise insert to the right of that control (index + 1).
If the button is added to an X-Y layout, then the index doesn't matter that much. You can simple just set the button's location relative to the mouse plus the x-offset, and y-offset.
As the mouse is dragging, you will need to force the controls to refresh. I think calling Invalidate() on the container control should be sufficient.
This should give you the basic idea that you could use to start coding something.