The layout editor is used for widgets and quick actions and lets you add, remove, move, and customize the buttons and other controls that you want to show.
Use the button bar to edit the layout. Press the icons the activate the different modes (add, move, delete, edit).
Press the plus icon to activate add mode. Pressing the plus icons on the screen will let you add new controls to an existing row, or add a new control to a new row.
Press the "move" icon to activate move mode. Select the control you want to move, and then press the left or right arrows to move the control. Press the "gear" icon to move rows.
Press the delete icon to activate delete mode. Select a control to remove it or, or press the "X" icon to remove the entire row.
Press the pen icon to activate edit mode. Select a control to access the property editor for that control. Follow the Property Editor tutorial for more details.