Sstrhsrtj

I am new to Latex and struggling with understanding of userpackages, .sty, .tfm, etc files.

I have a requirement to create PDF with latex equations in Spanish,Chinese and Japanese.
What I have tried till now :

I tried creating document using Spanish using following code

documentclass{article}
usepackage[utf8]{inputenc}
usepackage[spanish]{babel}

begin{document}

tableofcontents

vspace{2cm} %Add a 2cm space

begin{abstract}
Este es un breve resumen del contenido del
documento escrito en español.
end{abstract}

section{Sección introductoria}
Esta es la primera sección, podemos agregar
algunos elementos adicionales y todo será
escrito correctamente. Más aún, si una palabra
es demasiado larga y tiene que ser truncada,
babel tratará de truncarla correctamente
dependiendo del idioma.

section{Sección con teoremas}
Esta sección es para ver qué pasa con los comandos
que definen texto

end{document}

using pdflatex.exe spanish.tex in command prompt, it gave an error of .sty missing file. During installation of miktex, I had selected the option to download when needed, but it does not download when required and gives FATAL error in the log file.
So, I searched that file on net and kept it in the same location as pdflatex.exe.
The spanish.pdf was generated.
Similary, I tried for Chinese lang data in the tex file.
But if gave lots of missing files - CJKutf8.sty, CJK.sty, CJK.enc,UTF8.bdg,UTF8.enc etc.
I downloaded them from net but always some or the other file is missing

Chinese pdf document creation questions:
1) I want to know, for a specific language where can I find all the packages that are required? so that I can download them once and then create pdfs
2) Where should be location of the prerequisit files? Once I download the files where should I keep it so that pdflatex.exe will be able to navigate it for that language?
I found that in C:Program files/Miktex 2.9/ there are folders for Babel-English, Babel-Spanish. But nothing for other languages. So, am not clear of where should I paste language specific pre-requisits

I hope the techies will reply with a layman answer at their earliest.
I could not get document for multi-language support for latex as well... If you have something related, please send me the link.

Thanks in advance...