Select the atom/atoms you would like to change with the Select tool, and then type the chemical symbol on your keyboard, or use the buttons on the Atoms toolbar.
Right-click the atom and change the atom type in the Atom Properties dialog window.
Select another bond type from the Bonds combo box and click the bond to be changed.
Right-click the bond and choose another bond type in the Bond Properties dialog window.
Place a template on the canvas by selecting a template from the Template Toolbar and click on the canvas. Predefined abbreviated groups can be also useful to create complex molecular structures.