Arduino(or Genuino if your in Europe like me) is an open-source project for people who want to get into electronics and programming. It comes with its own C based language called Arduino. There are various different types of Arduino. Beginners should use the Arduino Uno, advanced and mediocre people should use Arduino Mega and Arduino Due. Arduino is open-source which means anyone or a any company can make their own version of the Arduino boards and sell them to consumers. Sometimes these Arduino's can be unreliable and might not work with your computer(I have had this experience before) so if your new, I suggest you get a proper Arduino board online or in an electronic shop that supplies Arduino's. If your new to electronics and programming and want to get started straight away you should get other electronic components to build some projects. You should get some LED's, resistors, capacitors, buttons and maybe even a screen

If your able to wait a while I suggest you purchase your extra components on eBay or amazon, they are a lot cheaper than at retail stores. If your short on cash and only want to the bare minimum then you only need an Arduino, you can write to the LED on pin 13 that is built in, but thats no fun. Some of the projects I found fun were police lights and traffic lights with LED's and sometimes a button. When I got more confident with Arduino and the Arduino language I began to make my own little handheld computer(I'm still working on it 3 months later) I used the Nokia 5110 screen, 8 buttons and some resistors on a breadboard. I wrote a ton of code and uploaded it to the Arduino. It works fine and I can do various things like play games and load code from an SD card.

Should I get an Arduino?

Yes! I would definitely recommend an Arduino board over an Intel or Raspberry Pi board for making your own electronics. The language is simple, it has short circuit protection and there are countless amounts of libraries available to download and make anything work with an Arduino. The thing I like most about the Arduino over the Raspberry Pi, is the fact that it has LABELED I/O pins. Its a lot easier to work with when you have labeled pins instead of having to look up a pin-out sheet every time you want to use your board.
Here is the link to the official Arduino site