Welcome to CYS. =)
Best place to start is the Help & Info section. There are several articles there that explain a lot about the storygame editor, commenting, the forums, trophies, exc. They also offer advice to new writers / members in general. It's definitely worth a read.
If you have any specific questions, asking on the forums should get you a good answer; the community here is very helpful and often quick to respond. You can also get help with beta-reading, or get advice / opinions on a story without having to publish. (I'd strongly discourage creating demos here, by the way.) Also, feel free to drop me a line personally. (Sending personally messages is explained in a help and info artcles.) I can answer most questions and if I can't answer one, then I know someone else who can.
I'd definitely recommend reading through the featured games in the storygame section. Partly because they're fun games and partly because it'll give you some ideas for what you can create one here. Lastly, if you'd like to practice your writing before trying your hand at a game, I'm hosting writing exercises Monday through Friday. Anyone is free to try doing them at any time, but if you want to earn points, you need to request to be added to the tag and scoring list.
Good luck and have fun.
