I would to ask ..if I want to learn programming arduino .... what should I start with ..and how?!

Answer 1

C++ The arduino Ide lets you program the microcontroller (board) in C++.
A library takes care of including your code in the main() function that you will never see using the IDE. The best way to start is by trying the examples provided with the IDE, editing the code and seeing it alive on the microcontroller.
The reference of the IDE is another good place for small examples.
SoloLearn C++ course is a good reference for functions and OOP that you can implement in your code.

Answer 2

i made a simple autonomous arduino robot with a random brain, pretty fun project. while i was trying to make it work i realised that u gonna need to separate the functions of your code, and the way to do that in the arduino IDE is to use tabs. creating them is as easy as clicking the + button on top but, one thing i had trouble was that, the code gets merged, or concatenated in the same order the tabs are created, so if u mess that order the code won't work t way u want.

another way to organize your code is to learn to create a class in C++ and add the files to t project folder and import it in the IDE, but you need to make a header file too. thoses things are explained on sololearn cpp course.