Students here you have full explanation.
Primero, sobre los adverbios en general. A continuación, sobre "comparison of adverbs".
Espero que os sea de ayuda.
Seguiré publicando sobre los otro puntos del tema de la introducción, así no hay que comprar tantas fotocopias!!!

1. The adverbs and the adjectives in English

Adjectives tell us something about a person or a thing. Adjectives can modify nouns (here: girl) or pronouns (here: she).

Adverbs tell us in what way someone does something. Adverbs can modify verbs (here: drive), adjectives or other adverbs.

adjective	adverb
Mandy is a careful girl.	Mandy drives carefully.
She is very careful.	She drives carefully.

Mandy is a careful driver. This sentence is about Mandy, the driver, so use the adjective.

Mandy drives carefully. This sentence is about her way of driving, so use the adverb.

2. Form

Adjective + -ly

adjective	adverb
dangerous	dangerously
careful	carefully
nice	nicely
horrible	horribly
easy	easily
electronic	electronically

Irregular forms:

adjective	adverb
good	well
fast	fast
hard	hard

If the adjective ends in -y, change -y to -i. Then add -ly:

• happy – happily

but:

• shy – shyly

If the adjective ends in -le, the adverb ends in -ly:

• terrible – terribly

If the adjective ends in -e, then add -ly:

• safe – safely

► Not all words ending in -ly are adverbs:

• adjectives ending in -ly: friendly, silly, lonely, ugly
• nouns, ending in -ly: ally, bully, Italy, melancholy
• verbs, ending in -ly: apply, rely, supply

There is no adverb for an adjective ending in -ly.

3. Use of adverbs

3.1. to modify verbs

The handball team played badly last Saturday.

3.2. to modify adjectives

It was an extremely bad match.

3.3. to modify adverbs

The handball team played extremely badly last Wednesday.

3.4. to modify quantities

There are quite a lot of people here.

3.5. to modify sentences

Unfortunately, the flight to Dallas had been cancelled.

4. Types of adverbs

4.1. Adverbs of manner

• quickly
• kindly

4.2. Adverbs of degree

• very
• rather

4.3. Adverbs of frequency

• often
• sometimes

4.4. Adverbs of time

• now
• today

4.5. Adverbs of place

• here
• nowhere

5. How do know whether to use an adjective or an adverb?

John is a careful driver. – In this sentences we say how John is – careful. If we want to say that the careful John did not drive the usual way yesterday – we have to use the adverb:

• John did not drive carefully yesterday.

Here is another example:

• I am a slow walker. (How am I? → slow → adjective)
• I walk slowly. (Ho do I walk? → slowly → adverb)

6. Adjective or Adverb after special verbs

Both adjectives and adverbs may be used after look, smell and taste. Mind the change in meaning.

Here are two examples:

adjective	adverb
The pizza tastes good. (How is the pizza?)	Jamie Oliver can taste well. (How can Jamie Oliver taste?)
Peter's feet smell bad. (How are his feet?)	Peter can smell badly. (How can Peter smell?)

Do not get confused with good/well.

• Linda looks good. (What type of person is she?)
• Linda looks well. (How is Linda? – She may have been ill, but now she is fit again.)
• How are you? – I'm well, thank you.

One can assume that in the second/third sentence the adverb well is used, but this is wrong – well can be an adjective (meaning fit/healthy), or an adverb of the adjective good.

Conclusion:

• Use the adjective when you say something about the person itself.
• Use the adverb, when you want to say about the action

Grammatical constructions used for comparing adverbs

There are three forms of comparison:

• positive
• comparative
• superlative

1. Comparison with -er/-est

hard → harder → (the) hardest

We use -er/-est with the following adverbs:

1.1. all adverbs with one syllable

positive	comparative	superlative
fast	faster	fastest
high	higher	highest

1.2. the adverb early

positive	comparative	superlative
early	earlier	earliest

2. Comparison with more – most

adverbs ending on -ly (except: early)

positive	comparative	superlative
carefully	more carefully	(the) most carefully

3. Irregular adverbs

positive	comparative	superlative
well	better	best
badly	worse	worst
much	more	most
little	less	least
far	farther	farthest
	further	furthest

ATTENTION!

In informal English some adverbs are used without -ly (e.g. cheap, loud, quick).

There are two forms of comparison possible, depending on the form of the adverb:

• cheaply → more cheaply → most cheaply
• cheap → cheaper → cheapest