u write a code, either in assembly or preferably in C language, use a burning software to convert that code into Binary data stream, which then can be burnt onto a microcontroller through an external burning device usually connected to computer throu serial or parallel port, USB enabled burners are also available but cost 6 7k rs i think.
counter IC ( integrated ciruit ) are small devices, u give them power, and a click input, and they will start counting, depending on the number of bits and type of counter. 0000 0001 0010 0011 so on. these patterns can then be used to turn on different combinations of LEDs