LaTeX is a programmation language which allows to produce some beautiful scientific documents. Contrary to Word, LaTeX is completely free of charge and is available on any OS (installed by default on every recent Linux or MacOS, to be installed on Windows). Furthermore, it is not really a WYSIWYG software since it is based on a specific code you have to write and compile in order to produce the final document in DVI, PostScript of PDF format.
Most Linux OS include a LaTeX distribution by default (e.g. TeXlive) In the contrary case, one will need to install a complete LaTeX distribution before writting any document. This is not the case for MacOS or Windows OS that do not embed any native LaTeX distribution.
Concerning MiKTeX, choosing full install is highly recommended even if it is time and memory consuming. Indeed, adding packages after the main install with MikTeX is quite difficult.
Reminder : for installing a software on a Linux OS, it is recommanded to use the package manager (Synaptic, Yum...).
1. Open a terminal and type the command
$ texhash1. In return, the computer will inform you which are the directories which contains the LaTeX packages.
2. Download the package you want to install : generally, you can find it on CTAN.org.
3. Unzip the archive file and deposit the files into one of the directories mentioned in step 2.
4. Type the command
$ texhash5. Your package is now taken into account.