Open the Selection combo box.
Rectangle selection : Provides easy selection when the fragments can be drawn around with a rectangle. Hold the mouse button while selecting; release the mouse when you are ready.
Freehand selection : Hold the mouse button and move the mouse pointer around the fragment you would like to select, then release the mouse button.
To select an atom, bond or group , click or select it (while the active tool is either the Rectangle selection or the Freehand selection ).
To select a structure, double-click an atom or a bond of it while the active tool is either the Rectangle selection or the Freehand selection.
One atom, or bond:
To delete an atom or a bond, click the Delete Tool on the Tools Toolbar, then click the atom or the bond. Alternatively, you can select the parts you would like to erase by holding the left mouse button and dragging.
You can delete a previously selected area by clicking on the Delete Tool or pressing the Delete key.