What is a Dossier?
When you create a Solution, the first thing you are presented with is a green button that asks you to add a Dossier (pronounced DOS-ee-ay).
A Dossier is a relational construct containing a Parent list and several Child lists. You can think of it as a case file or a folder; one of its purposes is that you can put an entire Dossier through an approval process, for example, without needing to process each of its entities separately.
Add a Dossier
Click Add a Dossier. A wizard will guide you through the process.
Main list
The first step is to specify your Main (Parent) list. This is the list that will drive your solution. The customized New Form on this list will likely be the one that people will open to create new entries related to your solution. For example, in an Expense tracking solution, the Main list would be called something like Expense Claims. In a Leave Request solution, the Main list would be called something like Leave Requests.
You can create a new SharePoint list in this step, or if you already have this list on your site, you can choose to Select an existing one at the bottom of the screen.