The Inputs tab is found both when editing/creating a Blueprint and a Vessel. The contents of this tab changes based on which element you are viewing.
When editing or creating a Vessel, the Inputs tab contains both the full visual description of a Blueprint (left) and all of the User Inputs (right) that need to be filled out in order to build a Vessel.
When editing or creating a Blueprint, the Input tab contains the variables to allow for user input (left), a description of the Blueprint (left), and a preview for validating the look and feel of the Blueprint (right).
These fields allow a user to input data that a script uses, without the need to code.