has to work simultaneous , not 1 before other, thanks
First concept to understand for a arduino AVR microprocessor is that it is a single 'core' processor and can only execute code one step one at a time, there in no 'simultaneous' capability. However the speed of execution can be such that many functions can execute 'independently' from other functions in your sketch as long as there are no 'blocking functions' being used, and delay is one example of a blocking function. Usings the millis() function is one way to setup time interval testing such that one's sketch can determine if enough time as passed or not for any given user function and just skip it if not or process the function if it has. Blink with delay is just one simple example of how one can structure one's code to avoid a blocking function like delay().