Data Element is a part of Elementary Types with global type, which use at all Field (in Table) and to be reference data type in ABAP program.
Steps to make Data Element
1. Open t-code SE11
2. Activate Radio Button 
3. Insert Data Element Name, initiate with letter Z or Y
4. Click Button 
5. Choose Data Element, then Click Button 
6. Fill in Short Description. Then fill in Domain if you want to use data type from Domain. But if you want to make data type then activate Built-int type.
7. Activate Field label's type then Fill in Field label as requirement, for finish press enter.
8. Click Button 
9.Package is filled to make Transportable Data Element into other client, but you don't need to fill it if practice only.
10. Click button to make Transportable Data Element into other client. Click button 
for practice only.
11. Click button 
to activate Data Element