This transformation works together with Call or Iterate table transformation. It obtains input dataset of such transformation of the other project that called current project. If current project was not called from another project then Input returns empty dataset.
To simplify development, it is possible to paste test data from the clipboard into Input transformation, similarly to Sandbox transformation. Typically, a small subset is pasted and then used for designing transformation. The pasted data is not saved and doesn't survive project re-opening.