A program is a collection of instructions that tell a computer how to perform a special task.
For example, it is like guiding you to make a menu, or directing a traffic policeman (or a traffic sign) to drive all the way to the destination. Without these special instructions, the expected task will not be carried out. So is the computer. When you want a computer to do something for you, the computer itself can't actively work for us, so we have to give it instructions, and it can't and can't understand the description of things in human natural language at all, so we have to tell the computer what to do and how to do it with programs. Even the simplest tasks need instructions, such as how to get keystrokes, how to put a letter on the screen, how to save files on disk, and so on.
So much trouble, even programming these things should be considered! No wonder some people say that programming is so difficult! You are wrong. In fact, many of these instructions are ready-made, contained in the processing chip and embedded in the operating system, so we don't have to worry about their work. It's all done by the processor and the operating system, and we don't need to get involved in these processes.
The computer mentioned above will not do anything on its own initiative. Therefore, we should make the computer "serve" for us through the program. And this process is made up by ourselves. Programming can be realized by using a programming language, and what the computer is required to do is described according to the grammar of this language.