Top notes: The scents that are perceived immediately on application of a perfume. Top notes are usually lighter, more volatile aromas that evaporate without delay. They form first impression of a perfume also called the head notes. Their scent usually remains for between 5 and 30 minutes.
Middle notes: The scent of a perfume that may be evident from the start, but will usually take 10-30 minutes to fully develop on the skin. They are the notes that classify the perfume family (floral, oriental, green, etc, see above). The middle note compounds form the "heart" or main body of a perfume and act to mask the often unpleasant initial impression of base notes, which become more enjoyable with time. Sometimes they are also called the "heart notes".
Base notes: The scent of a perfume that appears close to the departure of the middle notes. The base and middle notes together are the main theme of a perfume. Base notes bring depth and solidity to a perfume. Compounds of this class are those with the greatest molecular weight and are usually not perceived until 30 minutes after application. Common base notes include oakmoss, patchouli, woods, musk and vanilla.
The scents in the top and middle notes are depended on the base notes, as well the scents of the base notes will be altered by the type of fragrance aromas used as middle notes. Manufacturers of perfumes usually publish perfume notes and typically they present it as fragrance pyramid, with the components listed in creative and abstract terms.
Different fragrances are suitable for different age groups or for different circumstances. For a young woman green scents are more suitable than oriental ones. But for the evening meetings or dates you should wear heavier, more sensuous types rather then light ones which, in turn, are suitable for daylight use.
Also don't wear one perfume all year all. Temperatures have an effect on the scent. Cold temperatures decrease the strength of the perfume so wear stronger scents in the winter. And vice versa, in the summer wear lighter scents.
Remember that perfumes can be fun to wear, but starting a new perfume always use it on only one small area of skin. If there is an allergy to any of the ingredients it's the safest way to realize it. After an hour, if there is no negative reaction, the perfume is safe to wear. Once you open a bottle of perfume, wear it! It will keep indefinitely when not opened, but... once the air has infiltrated into the perfume, it must be used within a year or two at the maxium.