I'd start with HTML.
I believe the first step is finding out what kind of things you want to develop. Each language is used for very different things and work in very different ways—while sharing similar semantics and syntax.
Learning HTML, CSS, or JS might not do you as good if you want to build games, while learning C# won't be very helpful when trying to build websites. Of course, learning anything will harness your skills and make it easier to teach your brain other languages.
I'm a web developer, so I'll always recommend starting with HTML, JS, and CSS and learning how to build website... but Python is widely referred to as a good starting base because it uses a syntax that is common across many languages and can be deployed for various uses from games, to desktop-apps, to web-apps.
The quickest way to learn is to get your hands on a computer and start completing free courses like these.
I hope that helps point you into the right direction!