How to select objects
Click to select
Click to select a unselected object under mouse. If there are multiple objects under the mouse, click again to switch the selected object in a selection. Click on blank space to end a selection. When no Shift or Ctrl key pressed, click on blank space will clear all previous selections.
[Shift] Key
Multiple selection mode, the previous selection will not be cleared even clicked on blank space.
[Ctrl] Key
Multiple selection mode, select all objects under mouse with a single click.