It is hard to describe a flavor or aroma in words. Fortunately, many
esters and phenols have flavors that strongly resemble foods or
substances that most people are already familiar with. For instance:

ISOAMYL ACETATE is an ester that smells like bananas or pears
ETHYL ACETATE is an ester that smells generally fruity, or in higher
concentrations like nail polish remover (because it is one)
PHENYLETHYL ACETATE is an ester reminiscient of roses or honey

These are common ones in beer, but there are others that generally
tend toward fruity, solventy, or even cheesy/sweaty. In my experience
the esters become much more apparent the warmer the beer gets.

Phenolics also can be related to other substances. Phenolics are a
very broad group of compounds--but I believe that when the word is
used commonly to describe tastes in beer, though, it's usually meant
to refer to phenolic compounds that create spicy or medicinal flavors:

4-VINYL-GUIACOL tastes like cloves or similar spices
4-VINYL-PHENOL can also be spicy
CHLOROPHENOLS taste medicinal (to me almost mouth-numbing)

General flavors in this group are spicy, peppery, smoky, or medicinal.

One way to learn these flavors is by tasting beers known to have
them. Of course fresh German hefeweizens are known for their banana
esters and clove phenols. Some readily available beers that are
estery without being phenolic are Fullers ESB or Youngs Special London
Ale (make sure they are fresh or the esters may be diminished). Beers
that are phenolic without being estery may be harder to come by. Some
witbiers may fit the bill, as will old German Hefeweizens that have
lost their banana esters. To me De Konnick is also pretty phenolic
when found on tap in the US, without lots of esters.

Hope that helps.

Baums