When you perform the initial Clio > NextChapter sync, new cases will be created in NextChapter for any bankruptcy matter you have in Clio and new contacts and bankruptcy matters will be created for any case you have in NextChapter.
If you have any cases already created in NextChapter that correspond to existing cases in Clio prior to the sync, you can select to connect the two cases when do you sync to Clio for the first time. This will prevent duplicate cases from being created in both programs and it will connect the cases so that information properly syncs anytime information is update in one system to the other.
To sync two cases, you will need the Matter ID Number from Clio. You can get this from the Matter URL when you're in the Matter in Clio here: