Welcome to the site! I'm glad you already started reading some of the stories, analyzing them is usually a good way to start to understand how storygames work. While you're at it you can also rate and review them, feedback is always appreciated.
As for your own writing, take a look at the articles in the Help & Info section and don't rush it. No one is timing you, you can take all the time you want to prepare and write your story. I'd suggest starting with something of small-medium size; storygames can become cumbersome branching things and it's better if you begin with something you'll actually finish. Make sure to proofread and polish your work before publishing, that is something that usually makes a good impression on the readers. If you have any writing doubts about your story, feel free to ask and share in the Writing Workshop.