Visual Studio Code

I am new to programming. I have started to use VSCode for projects here. At first it was only for HTML but I recently started to work in C#. But how whenever I want to open a new project to code in HTML, it automatically opens with C#. Anyone knows how to switch languages in VSCode?

Do your files have a file extension? It should auto detect based on the file extension, assuming you have that language installed in Vs code.
See here for Visual Studio Code Docs, which contains how to change/check the language mode for the file you are in and how to change your settings to associate file extensions with a language.