In order to migrate your stories to the new FF section there are numerous steps to be followed. The process to migrate stories from the old FF section to the new and the process to migrate stories from the other forums to the new FF section is different.
Migrating from the Fan fiction forum
1) Click on fiction you want to migrate and locate the "migrate" option. Click on the option.
2) Once you click on the migrate option you will have to select the posts you want migrate. Click on the migrate option below the page once you're done.
3) Your editing page on the new section looks something like the below. Edit your status, the title of your book, the cover and your summary. At the end of page you have space to input your couple and shows tags.
4) You can also edit your chapter update, change the order, add a new chapter and much more.
Migrating from other forums
1) Go to the new fan fiction site.
2) Click on create a new story (the icon is present in the top right side)
3) Write the name of your story that you need to download and press edit button present below.
4) In the edit, page click on the migrate from another topic. You will find forum option and then whatever you posted in that forum. Click on the desired link and press ok.
5) Click on the chapters you want to migrate and then you are done.
6) Make sure to change your story status from draft to ongoing or completed so that it is accessible to your readers.
If any time you need help regarding your migration, feel free to contact the Fan Fiction Editors. You will be able to find the link of their profile on the main page.
For a detailed process explanation with pictures please visit the thread