You can create data elements either in the integrated SAP GUI or using the creation wizard of the form-based editor if your Eclipse-based IDE is connected with SAP NetWeaver 7.5 SP00 or higher.
The inactive version of a data element is created and stored in ABAP Dictionary. In the Project Explorer, the new data element is added to the Dictionary folder of the corresponding package.
The form-based ABAP Dictionary editor is opened. Here you can edit the data element.