A systematic name isn't labelling a molecule — it's a set of step-by-step instructions for rebuilding it from scratch. Longest chain, lowest numbers, alphabetical substituents: do them in that order and the name writes itself. Pick a molecule below, then raise the building progress and watch its name build step by step.
For a simple unbranched alkane, the name is straightforward: count the carbons in the chain, apply the prefix (meth-, eth-, prop-, but-, pent-, hex-, hept-, oct-), and add "-ane" as the suffix. But this simplicity is deceptive — the real power of IUPAC naming only becomes clear when molecules get complex. A six-carbon chain is hexane. A seven-carbon chain is heptane. The suffix "-ane" tells you it is a saturated hydrocarbon with only single bonds. The system is designed so that every molecule has exactly one correct name, and every name describes exactly one molecule.
The longest chain containing the functional group becomes the parent name, you number to give the functional group the lowest position, then name substituents alphabetically with their position numbers — the suffix comes from the highest-priority functional group.