A programmer is a specialist who creates the source code for a program. Such a program can be a computer operating system, a video game, a web or mobile application, and even a microwave algorithm. The program code is written in a special programming language.
Today, there are several hundred programming languages, but the most common ones are Java, Python, PHP, C#, JavaScript, C, C++, Objective-C, and Swift. Which programming language to choose, the programmer decides for himself, depending on the specific task (to make a game, an application for the web or a program for the server) and his own knowledge.