Issue: How to add new chapters to a story?

So obviously I'm new here, and I'm totally confused of something. I have no idea how to add a new chapter to my story I recently created! The layout is a bit confusing to me! I've seen, from reading other stories, how on each page/chapter there is a key of sorts where you can simply click on whichever chapter you want to go to. I have no idea how to make this happen for me!!! How do I add a new chapter?! Help please! It's most likely something easy I'm overlooking, I'm just so paranoid about somehow messing up my story I submitted that I'm scared to do anything! lol