1) IDocs or Intermediate Documents allow different application systems to exchange structured business documents through a standardized format. They consist of control, data, and status records.
2) Common uses of IDocs include electronic data interchange (EDI) between SAP and non-SAP systems, and application link enabling (ALE) for integration between SAP systems.
3) Key TCodes provided for working with IDocs include WE30 for creation, WE05 for overview, and BD87 for reprocessing. Detailed steps are outlined for creating a new IDoc type from defining segments to linking a message type.