The Degrees of Comparison in English grammar are made with the Adjective and Adverb words to show how big or small, high or low, more or less, many or few, etc., of the qualities, numbers and positions of the nouns (persons, things and places) in comparison to the others mentioned in the other part of a sentence or expression.
An Adjective is a word which qualifies (shows how big, small, great, many, few, etc.) a noun or a pronoun is in a sentence.
An adjective can be attributive (comes before a noun) or predicative (comes in the predicate part):
e.g.  He is a short boy. (‘short’ —  adjective – attributive)
This boy is short.  (‘short’ —  adjective – predicative)
An Adverb is a word which adds to the meaning of the main verb (how it is done, when it is done, etc.) of a sentence or expression. It normally ends with ‘ly’, but there are some adverbs that are without ‘ly’:
e.g.  She ate her dinner quickly.   He writes neatly.  They type slowly.

Kinds of comparison:

1. POSITIVE DEGREE: 
Example: Jacob is tall a boy.
In this sentence the word ‘tall’ is an adjective telling us how Tom is.  There is no other person or thing in this sentence used to compare Tom with, but it is the general way of saying about persons, animals and things that they have some quality (here ‘tallness’) above average in general sense. The adjective word ‘tall’ is said to be  in the “positive form”.
This comparison is called “positive degree” comparison.
There are two more comparisons with the ‘positive form’ of the adjective words. They are:
(i)  Degree of Equality: This comparison is used to compare two persons, animals or things to tell us that they are equal – having the same quality.
Example: There are  two dogs with the same height and weight, and look the same except for the colour.
The word “beautiful” is an adjective in the ‘positive form’, and with the conjunction as…as  it expresses the ‘degree of equality’.
(ii)  Degree of Inequality: This comparison is used to compare two persons, animals or things to tell us that they are not equal – not having the same quality.
The brown cat is not so beautiful as the black & white cat.
The word “beautiful” is an adjective in the ‘positive form’, and with the conjunction so…as (and the negative ‘not’) it expresses the ‘degree of inequality’.

2. COMPARATIVE DEGREE:
There are two more degrees of comparison with the ‘comparative form’ of an adjective. They are:
(i)  Parallel Degree: This comparison is used to show that the qualities of two items (adjectives or adverbs) talked about in the given sentence go parallel, i.e. if one quality (adjective or adverb) increases, the other quality (adjective or adverb) increases, and if one quality decreases, the other quality also decreases.
Example: The bigger the box, the heavier it is.
(ii)  Progressive Degree: This comparison is used to show that the quality of a thing (adjective or adverb) talked about in the given sentence increases as the time passes, for example:
It’s getting hotter and hotter day by day. 

3. SUPERLATIVE DEGREE:
This comparison is used to compare one person, animal or thing with more than two persons, animals or things (the rest of the group of more than two), and to say that the particular one has the highest degree of that particular quality This comparison is called “Superlative Degree”.
Example: The blue whale is the largest of all animals.