The organized collection of machine instructions, i.e., program is written in an appropriate programming language that the machine can interpret and execute
Program may have thousands of millions of put together and stored in the memory.
Control subsystem control the program to execute instructions by instruction.
So software engineers or programmers develop the program and is stored in the memory with the help of input subsystem.
And the program is executed and the end user interacts with the computer and do the tasks.