Programming Languages

The term Arduino is related to electronics field which is totally different from your field whereas programming is done on C+. Arduino is an open-source platform used for building electronics projects. Arduino consists of both a physical programmable circuit board (often referred to as a microcontroller) and a piece of software, or IDE (Integrated Development Environment) that runs on your computer, used to write and upload computer code to the physical board. You have to start from PCB board, you have to know how diodes and transistor work. You have to go through the basics of Arduino not only Arduino but also electronics basics.
Download Arduino Software:
You'll need to download the Arduino Software package for your operating system from the Arduino download page.
Microcontroller:
Arduino is a microcontroller on a circuit board which makes it easy to receive inputs and drive outputs. A microcontroller is an integrated computer on a chip.
Inputs:
Some examples of inputs would be a temperature sensor, a motion sensor, a distance sensor, a switch and so forth.
Outputs:
Some examples of outputs would be a light, a screen, a motor and so forth.
TL, DR:
Arduino is a small computer that you can programme to read and control electrical components connected to it.
Obtaining an Arduino Board:
There are several online distributors that stock Arduino boards.