I wanted to develop software for custom arduino electronic board. I wanted the software to install on Windows, and to be user friendly (meaning people without knowledge of electronics can use it to modify the circuit board parameters). What programming language should I use and is there some reference how to do it? Is it a C programming language?
Sorry, but you need to do a lot more research.
Arduino is a product which consists of a large library for programming from their IDE and most often an 'AVR" brand microprocessor with a specific 'bootloader' pre-installed.
Programming is done in C, but is often masked behind the pre-built functions that are bundled in the library that is supplied with the Arduino Software packages.
You can quite easily make your very own 'Arduino' by purchasing an AVR microprocessor, and flashing the 'bootloader' on it manually, then simply using their IDE.
So.. if you want to produce your own software for 'Arduino', what you actually need to do is produce your own GUI for their existing software, or build your own software for an AVR.
Alternatively, if you are building a board that will not be 'programmed' but simply 'tuned and/or adjusted' then you can build the board with any microcontroller you want. The software will simply communicate with the microcontroller which will then alter it's own settings.
(this is the difference between reinstalling Windows on your computer... and simply saving a different homepage... No need to allow them to 'program' the board unless you want them to be able to change EVERYTHING on the board... which could lead to damage of the board or controller if programmed incorrectly.
