Perfume is a solution of pleasant-smelling materials in solvent, usually alcohol plus water. A single scent would be rather boring. The mixture usually contains very volatile scents for the initial top note, less volatile scents for the sustained aroma, and persistent scents for the final end note.
Fixatives alter the rates of vaporization and hence the sustained scent development.
They are typically extracted from the whole, macerated, or ground up natural source with pure alcohol. Add the chemists' reaction flasks for almost anything imaginable. The trick is to mix the scents, sometimes dozens of them chosen from among thousands, to create something wonderful start to finish.