Yes, in order for your story to be discussed, you must submit it to the main site and have it approved for posting. We are not a pre-submission editing service, we're a group of people interested in discussing individual stories to learn more about writing and to enjoy critiquing.
Once your story has been approved, you open the thread at the top marked "Volunteer your story" and sign up there. Your story will eventually come around in the rotation.
We have one carved in stone rule. You must participate in another story discussion before your story will be discussed. If you don't--we check--you'll be skipped. It's very important that we give back to the community, not just take from it.
Non-SDC threads are moved to the appropriate forum.