Basically, the Selection Object is an object that will save selections in your object manager. For instance, I currently have a project that I need to keep adjusting groups of plain effectors, but are children of multiple objects scattered throughout my scene. I’m able to select them all at the same time, with this object. Great for dense scenes.
I have no idea where it is in the menus or if it is even a default menu item. Do a search for Selection in your customize window. You can add that tool to a palette.
The “huge” option when previewing materials is kind of a joke, since it only scales up your preview by a few pixels. If you right click on the preview image, you will find the Open Window option. View your preview however big or small you want, super handy.
In this tutorial I break down how to make the classic mario question mark box, using only one material and one cloner object, along with a few effectors.