There are a lot of articles in the Help & Info tab on creating story games and writing basics. Look under "storywriting" for topics like writing your first story, character creation, beating writers block, etc.
If the actual story is what you are having trouble with, I recommend putting your plan down on paper, and then just starting to write. Your plan could just be a list of the main plot points you want to hit in order, and then write from one to the next. filling in the details should be the fun part.
Are you thinking like a short story in the forum? or a story game CYOA?