Arduino IDE
The arduino board has a chip called ATMEGA328P made by Atmel (R). There are two versions of this chip: smd or as the usual chip. So, now we have the chip but we want to code it. But, we can't code it directly from c++ to it's code. We need a "translator" from c++ to the chip's language which is mostly the CH340 chip or the FT232. So now we can use a program that send c++ program to the translator and the to the chip. But, which is the program? The program is the ARDUINO IDE. It's and open source program that allows you to code and upload your code to the motherboard. If you want to try you arduino conect your arduino to your computer, then open the arduino IDE and select the port in which is the arduino. In the arduino IDE go to File > Examples > Basics > Blink and upload the code to the arduino. Now, you'll see that there's a led blinking in your arduino.