A program, in its essence, is a sequence of instructions that make the computer do a certain task. They are being entered by the programmer and are being executed unconditionally by the machine.
Watch a video lesson about runtime environments and programming languages here: https://youtu.be/ziG5v36lSVk.
Low level languages manage the hardware directly and require a lot of effort and a large count of commands to do a single task. Languages of higher level require less code for a single task, but do not have a direct access to hardware. Application software is developed using such languages, for example web applications and mobile applications.
C# is a compiled language, which means that we write commands that are being compiled before they're being executed. Exactly these commands, through a help program (a compiler), are being transformed into a file, which can be executed (executable). To write a language like C# we need a text editor or a development environment and .NET Runtime Environment (like .NET Core).
.NET Runtime Environment represents a virtual machine, something like a computer in the computer, which can run a compiled C# code. With the risk of going too deep into details, we have to explain that the language C# is compiled into an intermediary .NET code and is executed from the .NET environment, which compiles this intermediary code additionally into machine instructions (machine code) in order to be executed by the microprocessor. .NET environment contains libraries with classes, CSC compiler, CLR (Common Language Runtime – CLR) and other components, which are required for working with the language C# and run C# programs.
The .NET environment is available as a free software with open source code for every modern operating system (like Windows, Linux and Mac OS X). It has two variations, .NET Framework (the older one) and .NET Core (the newer one), but none of that is essential when it comes to getting into programming. Let us focus on writing programs with the C# language.
As we have already mentioned, a program is a sequence of commands, otherwise said, it describes a sequence of calculations, evaluations, iterations and all kinds of similar operations, which aim to obtain certain result.
A C# program is written in a text format, and the text of the program is called a source code. It gets compiled into an executable file (for example
Program.cs gets compiled to