What is the brain ?

First we have to know what is the brain

The brain is an organ that serves as the center of the nervous system  in all vertebrate and most invertebrate animals—only a few invertebrates such as sponges, jellyfish adult sea squirts and starfish do not have a brain, even if diffuse neural tissue is present. It is located in the head, usually close to the primary sensory organs for such senses as vision, hearing, balance, taste and smell.The brain is the most complex organ in a vertebrate's body. In a typical human, the cerebral cortex (the largest part) is estimated to contain 15–33 billionneurons each connected by synapses to several thousand other neurons. These neurons communicate with one another by means of long protoplasmic fibers called axons, which carry trains of signal pulses called action potentials to distant parts of the brain or body targeting specific recipient cells.

And now that we know what is the brain here comes the real question... Which is the difference between right and left hemisphere? 

The Right Brain

* Sees, thinks and processes information in whole, concrete images, therefore, it does not use a step-by-step method to reach a conclusion.

* Has difficulty understanding the parts of whole images without the whole object present. For example if a teacher is using an orange cut up into pieces to demonstrate fractions there should also be a whole orange in view of the student to keep the "whole" picture in their minds.

* Has difficulty thinking in sequences and has to be trained in sequencing skills, using concrete
 materials and visual aids. Examples of aids are: blocks with letters or numbers, flashcards, multiplication tables, coins for understanding money, clock faces with removable numbers, etc.

* The right brain is reality-based because it thinks in whole, concrete images; that is, it thinks in whole pictures and does not think in the abstract or parts. Therefore, it cannot work easily with abstract symbols like words and numbers.

* Thinks multi-dimensionally, or comprehending a subject on many different analytical levels. Therefore a right-brained person will not fully understand a concept until all aspects of the subject are put together to form the whole image or conclusion.

* Has difficulty focusing on and organizing a large body of information such as a school project with written material, drawings, photos, references, etc. This is because a right-brained person is always using a multi-dimensional thinking process and can get confused where to start on a project and how to put it together in a logical, step-by-step format.

* Thinks emotionally, intuitively, creatively, globally and analytically

* May have difficulty with the verbal or language arts skills of hand printing, phonics, spelling, reading, writing sentences and paragraphs

* May have a photographic memory for images, reading selections, oral discussions, places visited and musical works.

The Left Brain

* Thinks in abstract letters, numbers, written words and formulas

* Excels in mathematics, reading, spelling, writing, sequencing and the use of verbal and written language

* Is strongly verbal and reacts best to verbal input

* Responds well to phonics when learning to spell and read

* Handles sequencing of numbers, letters, words, sentences and ideas easily

* Does not need to visualize in whole, concrete images to understand ideas, both concrete and abstract

* Sees the parts within the whole first, then arrives at the whole concept of a given idea.