This is a basic primer to book publishing.
All you need to publish a book, really, is book design - you need:
Then you can upload those files to Createspace and Kindle, or (if you want) Draft2Digital or Ingramspark.
It can take time to get all the files finished; formatting usually takes longer than you expect - hopefully you won't find a whole bunch of typos or issues after you get it formatted - and the full print cover can't be made until that's done, because you need to calculate the spine width based on final page count.
A good designer will help get all the files right, but generally, you need to leave a time-buffer so you don't get too stressed out.
Once the files are approved, live on Amazon, you can start working on reviews, cleaning up your Amazon description, making sure your categories are right (you can email KDP support and get added to as many as 10 categories).
After everything is working and looks good, you can start promoting.