Main menu can be accessed by double-clicking on the empty white space of the editor.
The drawing mode allows drawing a carbon just by clicking on an empty field. Clicking on any existing atom will add an additional carbon. If you click on a single bond, you will get a double bond (clicking on a double bond will draw a triple bond).
This mode will allow you to move an atom or a bond just by clicking&dragging. If you double-click on an atom, the “atom menu” will open where you can change the element (for example from C to O), annotate it or adjust color.
You can also change the symbol just by hovering the mouse over the atom and typing the label. The editor will recognize names of the elements and chemical labels. For elements commonly used in organic chemistry, the valence will adjust automatically, changing the number of H atoms or charge when necessary (or showing red X). You can also type an entire group, e.g. “CH2F”, which should be properly recognized and counted in the molecular formula.
To see the molecular formula, click on the “Molecule” tab from the main menu and type {MF} in the “Format” field. Then check “Show label” and press “Apply”.
To import or export mol files, use the File menu from the top bar.
To convert an IUPAC name to the structure, choose “IUPAC” from the Tools menu. The list of compatible names can be found on the OPSIN website.