FinalBuilder's Design mode consists of three main sections:

Project / Action Types / Action Inspector

This section contains four tabs:

Action Lists

This is where you create and edit the actions of your project.  There are two built-in action lists, Main and OnFailure.  You can also add extra Working with the Action Types Panel.

Log/Script Editor

There are several tabs in the bottom section, but the most relevant ones during design of your project are the Quick Help.