Set a chain length, then hang branches on it. The drawing, the formula and the full IUPAC name update with every click. Watch the teal highlight: the longest chain is not always the one you drew.
Each corner and each loose end is a carbon atom. Hydrogens are left out of the drawing, because every carbon simply fills its four bonds with them. Gold numbers run along the chain the name counts from.
Condensed formula: CH3CH2CH2CH3