Not every submission is guaranteed to get in, the challenge is just to try and get people to start writing if they haven't had an opportunity to do so before now, and have the upside of getting their novel into the Tapastic app if it's good. Plus they're fun for the community to take part in, even if you just do it on your own and not send it in for the sake of writing
If you do submit your story, first and foremost the only people will be reading it are the Tapas staff; they won't post your novel to the app without your permission or without sorting it out with you first, so you don't need to worry about a bunch of community members on the website reading your novel if you don't want them to/aren't ready to reveal it to them yet 