How to use a Github markdown file to fill variables

This is my first post to Github Support Community. In case this is not the right place to ask this here, please consider.

Today I have been asked to use a markdown file to fill variables. But I don’t know how to do it.
I came through some of the tutorials and have realized that a Gitlab account is (probably) required, so created one.

But could not understand where to start, how it works and how I can replace those variables. Is there a proper step by step tutorial which I need look into?

I have created a NodeJS based application which is in Github but I need to add some variables in one of the markdown files.

I looked into the following articles so far:


Any help or suggestion from the community is highly appreciated.

Subrata Sarkar