http://www.engvid.com/articles-in-english-how-to-use-a-an-and-the-properly/

Comparisons

comparisons

when we compare two people or things

lThe easiest rule is: add the ending –er to one-syllable words and to two syllable words ending in –y, e.g.

lFast – faster

lEasy – easier

lBig - bigger

 

Comparisons involve at least two people

lpeople or two things. We use than before the second part of the comparison:

lPeter is taller than Jim

lThis car is faster than that one.

llonger words, e.g.

ldifficult – more difficult

linteresting – more interesting

lbeautiful – more beautiful

lIn sentences:

lMary is more beautiful than Sally.

lThis book is more 

lSome adjectives form their comparative and superlative degrees in two ways:

lold – older/elder – the oldest/eldest

lfar – farther/further – the farthest/furthest

llate – later – the latest/last

lnear – nearer – the nearest/interesting than that one.

lAs…as…

lJohn is as tall as Bob.

lYour house is as large as mine.

lNot so/as.. as..

lThis book is not so interesting as that one.

lThe tree is not as tall as the building over there.