[solved] how to add objects

in the (mostly new) level editor how do I add objects? I saw their is an asset browser but how do I get those assets into the map?
how do I add a new water plane and/or block without it removing itself from the scene tree?
^when I add a water plane, if i click on the object in the scene tree, it gets I presume auto-deleted.

 

Double click or drag-and-drop the .dae from the asset window to your map. And after selecting waterblock, click it to the map before going to scenetree.

 

thx m8