The difference between types of fragrance is the amount of oil concentration in it. The higher the oil concentration the longer your fragrance will last and the less you need to use.
Parfum has the highest oil concentration, causing the scent to be released over a longer period of time in a series of its notes. Then is Eau de Parfum which has slight lighter scent than parfum.
Following would be Eau de Toilette, whose scent is lighter, allowing you the ability to apply more.
Finally, Eau de Cologne is the most subtle version of fragrance; however Eau de Toilette and Eau de Cologne are generally interchangeable, in Men's fragrances and After Shave which have the least amount of oils. But keep in mind men fragrances typically use stronger notes.