Click the "+" icon and add two C (carbon) atoms. Each carbon atom will have four unpaired electrons.
Click the "+" icon to add six H (hydrogen) atoms.
Click on one unpaired electron of the first carbon atom and then on an unpaired electron of the second carbon atom to form a bond between the carbons.
Click on each remaining unpaired electron on the carbon atoms, then click on the unpaired electron of a hydrogen atom to form bonds. Repeat until all hydrogen atoms are bonded.