It is possible to mark the standard Transport Form and a Task fields as mandatory fields if required.
Some fields must be mandatory by default for the application to function correctly but others can be made mandatory if required. For example, the Group or Type might always need to be specified. If a mandatory field is not populated the Transport Form or Task cannot be saved.
Custom Fields are created and edited by TE Administrators via the TE Windows GUI screen configuration screen. [on the Fields tab]