A command is a complete SQL Select statement that will be in the format:
Select
<all of the fields that you need for the report>
from <primary report table>
<join any other tables for the report>
where
memotable.memofield like '%{?Rights}%'
and <any other selection criteria>
In the Command Editor, you'll also create a parameter called "Rights" - you MUST create it in the command editor NOT in the regular parameters for the report, although it will appear in the parameters list in the Field Explorer.
If you're not familiar with writing SQL, then I would recommend working with your DBA.
-Dell