Selected examples from the video:
When you mouse over a cell bracket seen on the right side of a notebook window, the mouse pointer changes shape, indicating that the cell can be selected.
The mouse pointer here is indicating that you can select the cell:
Select the cell by clicking its bracket. The cell here has been selected:
When the cell bracket is not visible, the mouse pointer still changes shape to let you select the cell. However, the selection is also not visible.
The cell here has been selected, but you cannot see the bracket or the selection:
Even though the selection is not visible, you can still change the properties of the cell.
Here, the background color of the selected cell with an invisible cell bracket was changed to light blue:
A cell with the ShowCellBracket option set to Automatic will display its cell bracket only when the mouse is over the bracket, thus allowing normal selection.
There is also another method for selecting cells, regardless of their brackets being visible or invisible.
Click between two cells, positioning the horizontal insertion bar there:
Press just once to select the cell below it:
Pressing just once would have selected the cell above the horizontal insertion bar. Repeating these keystrokes will continue to select cells in the direction of the arrow keys you use.