To create a cross project query:
The Artifact types in this project and saved lists table lists all artifact types in the current project and any saved lists of artifact types. The Artifact types in other projects table provides a list of all artifact types in all projects available to be added to your query. Projects are only available if you have permissions that allow you to query in that project. You can also select from a list of predefined searches for all projects as listed in the Predefined static cross project lists section.
This will move your selections to the Artifact types selected section. You can remove all selections from your query by clicking the Remove all button or remove only selected artifact types by clicking the Remove selected button.
This will take you to the Advanced query page where you can define your query criteria as you would for a single project query. (For further information on building queries, see the Advanced query help documentation).
If you choose to save your query you can now name the query and provide a brief description.