Installing the software
We have seen the downloading considerations for every operating system; let's now go on to see how to install the package for each of them.
Windows
Under Windows, using the Windows Installer package is quite simple and doesn't require any special consideration.
If you opted for the compressed package, you have to only uncompress it with an archive uncompressor such as WinZIP to make it available, which is not too hard.
Mac OS X
Under Mac OS X, the installation of the application consists only of dragging the application icon to the Applications folder of your computer. Simple.
In the latest versions of Mac OS X, Java may not be preinstalled; if this is the case, you should go to the Java official website at http://www.java.com/en/download/ and download it.
Linux
Given the diversity of different distributions and the packages' dependencies system on which Linux relies, you should install some of them before you can run the Arduino development environment.
Thanks to the package management systems based on centralized repositories present in most Linux distributions nowadays, it is even possible to install the Arduino development environment directly from a repository along with all the needed dependencies using just a command. It makes this the preferred way of installation if the available version in the repository is up to date.
In case of trouble
In case you encounter any problem during the installation process, you could go to the Arduino site and take a look at your corresponding operating system's Getting Started guide for more detailed step-by-step instructions at http://Arduino.cc/en/Guide/HomePage.