Learn about games. Play games you enjoyed again and try to figure out how they work and how they do what they do and why. Many game developers have blogs and web sites and Twitter streams. Subscribe to those and read what they’ve written in the past years. Search StackExchange here and just read any topic that talks about things you will need for whatever the simplest game idea you’ve had so far would need. Use your favorite web search engine and just type in any questions you have and see what interesting stuff you find.
This will give you a better idea of how game developers out there work, what tools they use etc. Then learn about those tools. Depending on what parts of game design you want to do, learn those disciplines (there are lots of non-game-development resources and tutorials about programming, graphics design, animation, sound design, UI design etc.).
There are also books about lots of game design topics.
In the end, it’s not important where you start, just that you start. Find out how to program your computer or how to install a development environment specific to games and start doing a few simple games, and keep trying things out, keep learning. Build a few to throw away, and thereby learn on the go.