What file uses .md extension and how should I edit them?

Question

On GitHub, several projects have README.md files. It seems like a simple format file to express text and pictures.

I guess there is an editor or syntax

Answer 1

Extension '.md' refers to Markdown files.

If you don't want to install an app to read them in that format, you can simply use TextEdit or Xcode itself to open it on Mac.

On any other OS, you should be able to open it using any text editor, though as expected, you will not see it in Markdown format.