[READ THIS]
Right so, although I do like bursting bubbles, I won't burst this one too much. Most of the people commenting are kind of accidentally lying to you, the reality is most of these methods just straight out won't work. There's a multitude of things you can do to learn about design and most of them are actually not game related.
See the thing is, most people when they want to learn about creating games, think the trick to learning about that process is by - creating games or writing sheets. I really, really disagree with that thought process.
In my experience, the trick is that you need to learn outside knowledge, learn about film, music, art, drama and writing. Honestly it is crazy, how many times, my studies of film and drama have actually been the initial structure I've had to use when I've had to create the foundations for a mod or simply explain a process to a studio. In my experience, I've found Pablo Picasso and Quentin Tarantino as great people to learn from when it comes to studying Film or Art. Picasso because of the way he views his world and Quentin because of how bold and different his approach is to creating a movie.
It's also best you avoid other people's methods for creating a sheet or making a game, because honestly - not only will your product end up worse, you'll lose an opportunity to develop your own confidence and learn something. Creating art requires you to take a very different approach then other people, you need to find a unique path that provides you with information that other people do not have and a vision that nobody else can think of. Because there is a similarity to creating games and cooking, the best cooks create things that are different and beautiful, bad cooks follow recipes and stay within the confines of cooking 'standards'.
But this should be something you want to do in the end, because there's no point spending your whole life learning about Design if this isn't the thing you live and breathe for. You need to ask yourself if this is something you could love, something that you think you have a passion for. This is a job you will be doing every single day for the rest of your life, it will essentially define who you are because you put so much time into it, so the last thing you want to do is to go down a road not meant for you. Figure out if you were meant to Design Games or if it's just because you want to do something 'fun', because most people get into games simply because they like playing games, which is not really a good reason to get in the first place, since basically the entire world likes playing games - there has to be a lot more to it then that.