@Anonymous
No secret button. In any subobject mode (i.e., vertex, edge, polygon, etc) of an editable poly/Editable mesh you should be able to left click on or region select (drag rectangle over ) the vertices,edges or polygons that you want. It looks like in the screenshot you posted, that you are in vertex subobject mode but that your display has edged faces turned off. I suggest you turn on edged faces (shortcut is F4) so you can see the edges. You should be able to left click or region select on any vertex, edge or polygon depending on which subobject mode you are in. The selected subobjects will be highlighted in Red. Are you saying that selection is not working for you?
