Adverbs and adjectives

Adjectives and adverbs are descriptive words, sometimes called modifiers because they restrict meaning. They add detail to statements. The difference between the two is that

• adjectives modify only nouns, pronouns, and verb forms used as nouns;
• adverbs modify verbs, adjectives, and other adverbs.

Adjective function: An adjective may be a single word: blue, tall, funny, warm. As a single word, it may come before the noun - the blue sky - or after the verb - the sky is blue. Adjectives may be positive (tall), comparative (taller) or superlative (tallest). Adjective phrases usually follow the noun they describe: the girl with blond hair. The phrase with blond hair describes girl. Adjective clauses also usually follow the noun: The child who finds the most Easter eggs wins. The clause who finds the most Easter eggs modifies child.
Adverb function: The most common use of an adverb, of course, is to describe verbs: He ran quickly. Actually, however, adverbs can modify anything but nouns (or verb forms used as nouns). Typically adverbs express:

• time (now, then)
• manner (happily, easily)
• degree (less, more, very)
• direction and place (there, up, down)
• affirmation or negation (certainly, not)
• cause and result (thus, consequently), and
• qualification or doubt (however, probably).

Although many adverbs are formed by adding -ly to adjectives (quick, quickly; happy, happily), adverbs have no characteristic form. They must be identified by the function they perform in a sentence. In the sentence That is a fast car, fast is an adjective. But in He ran fast, it is an adverb.
Certain adverbs (how, when, where, why, whenever, and wherever) are called relative adverbs because they introduce relative clauses in a sentence: The keys are upstairs where you left them. The clause where you left them modifies the adverb upstairs.
Other adverbs are called conjunctive adverbs because they join one clause with another. Some of these adverbs are: therefore, accordingly, besides, furthermore, instead, meanwhile, and nevertheless. In the sentence He was tired; therefore he stayed home, the word therefore modifies the clause of which it is a part and connects that clause to the previous part of the sentence. Note that therefore is not to be used as a conjunction, hence the semi-colon.

source:http://babelnet.sbg.ac.at/themepark/grammar/qualifier.htm