Click the "+" icon and add two C (carbon) atoms. Each carbon atom will have four unpaired electrons.
Click the "+" icon to add two H (hydrogen) atoms.
Click on three unpaired electrons of one carbon atom and then on three unpaired electrons of the other carbon atom to form a triple bond between the carbons.
Click on the remaining unpaired electron of each carbon atom and then click on the unpaired electron of a hydrogen atom to form two single bonds.