My advice is to start by creating the simplest game you can imagine. Normally people recommend Pong for such an activity because it can be done fairly easily.
Pick a tool/programming language and start creating a very simple game. This will teach you a lot about how games are constructed, the time they take to create, and it will help you to determine whether or not game development is really something you want to investigate further.
You can search these forums and the internet for similar questions as many people have asked the same questions as you. Look around and try to get a feel for just what it takes to make a game.
Also realize that the art of game design is rarely what you add, but what you can take away while maintaining your game's vision.
This is a journey that will take you a lifetime to complete. Expect to spend many years at this if you are serious about game creation.
Don't rush, start small, and have fun.