Hi Roberta,
In general in SHD0 you have to define a Screen Variant first.
After you have defined a scrren vairant this variant can be selected within the transaction via 'EDIT' > 'Screen Variant' > 'Select Screen Variant'.
In SHD0 you can then assign the Screen Variant to the Transaction Variant. There you have to define a name for the Transaction Variant and then you can assign the prior assigned Screen Variant to it.
In the last step you go to tab Standard Variant and enter the name of the prior defined Transaction Variant. After pressing the activation the variant is automatically taken in the related transaction for all users.
In general in SHD0 you have to work from the right tab to the left tab
1. Screen Variant
2. Transaction Variant
3. Standard Variant (for all users or user specific via groups)
I hope this helps you.
Pls also review attached notes for help
1885677 http://service.sap.com/sap/support/notes/1885677
1885760 http://service.sap.com/sap/support/notes/1885760
1886315 http://service.sap.com/sap/support/notes/1886315
br,
Gavin