Step 2: Create your ethene molecule

First we construct an ethene molecule, and preoptimize its geometry:

Select the C-tool by clicking on the button with the 'C'
Select the Double bond mode by selecting 'Double' from the bond menu
Click somewhere in the drawing area to create a carbon atom
Click again to create a second carbon atom (with a double bond)
Select the select-tool by clicking on the button with the arrow
Click once in empty space so nothing is selected
Select the 'Add Hydrogen' command from the 'Edit' menu
Click the optimizer button (the smiley)

Your ethene molecule should look something like this: