How to Download Arduino IDE
Download Arduino Environment
You can directly download the latest version from this link: http://arduino.cc/en/Main/Software. When the download is finished, unzip the downloaded file. Be sure to preserve the folder structure. Double-click the folder to open it. There should be several files and sub-folders inside.
The Arduino Software (IDE) allows you to write programs and upload them to your board. In the Arduino Software page you will find two options:
1. If you have a reliable Internet connection, you should use the online IDE (Arduino Web Editor). It will allow you to save your sketches in the cloud, having them available from any device and backed up. You will always have the most up-to-date version of the IDE without the need to install updates or community generated libraries.
If you would rather work offline, you should use the latest version of the desktop IDE.
Install the Arduino Desktop IDE
Portable IDE (Windows and Linux)
Choose your board in the list here on the right to learn how to get started with it and how to use it on the Desktop IDE.
You can check all the Arduino software of old version from this link: https://www.arduino.cc/en/Main/OldSoftwareReleases#1.5.x
Reference for Arduino Programming Language
Arduino programming language can be divided in three main parts: structure, values (variables and constants), and functions.
You can see more details on the following link: