How do I write about a character? Please be specific.

My answer will be a bit long.
:D

When writing about a character, you must take every part
of them into consideration.  How do they react the world around them: both natural and
material.  What do they like, hate, love, or feel neutral about?  How does their
ethnicity, religion, political views, etc. change their outlook on life?  Are they
serious or carefree?  What do they look like; are they intelligent; are they street
smart?  How do these things add up to their actions, thoughts, and inner psyche?  How to
other characters, readers, and writers view these
characters? 

Most importantly: how does the character move
the plot forward, change the plot, and/or handle the actions of the
story.

Describing a character ultimately stems from your
own perception of them.  What one person may see as a strong and lovable character,
another may see as being weak and boring.  Your opinion matters, but it is also vital to
try and scope out the writer's original intention.  Often this may conflict with your
own theory, and that is when you must decide whether or not to embrace the author's
point of view or stick to your original idea.

For example
(and this is my inner nerd coming out ;)), in Harry Potter, I LOVE
Severus Snape.  I see him as flawed but deeply beautiful: a man as gentle as he is
rough.  J. K.Rowling says that, for all his atonement and love for Lily, he is basically
not a nice guy: even though he is one of her favorite characters.  Now, I choose to
stick to my interpretation of Severus, even though it conflicts with the author's
intent.  That is the kind of thing that will be up to you.  Generally, I think that
author intent is vital, but there are times when one cannot help but see things entirely
different! 

Another example: Some people, even scholars, do
not read the sections of Dante's Vita Nuova that do not include Beatrice.  They feel
that those sections sully the romance and passion of the treatise.  I feel that it's
important to read the entire work.  It is not a work of fiction, and why ignore the
facts?  This is rather ignorant.  I may not like the fact that Dante wrote about women
who were not Beatrice, but it doesn't change
history. 

Overall, be critical and open-minded when writing
about a character.  Pay close attention to details.  Write with honesty and integrity to
your opinion.  Literature is often oh-so-subjective.  Find your
view and make a case for it.  You can't go wrong when you write about a character unless
you don't take the time to analyze them. 

Good luck, and I
hope this helps!