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

The easiest thing to do, if you do not have a reader, is to open the MD file with a text editor and then write the MD file out as an HTML file and then double click to view it with browser.