This feature will be expanded on in later Help files but essentially it is this.

This feature allows you to build select statements against tables which you can execute within the ITRDS Client. This can be done on local data and remote HTTP data.

To access this you go to the 'Queries' menu in the Data view as shown below

To create a new Query you have two options. Either select 'New' here OR you can right click on a table or view from the listings of Tables or Views in the Data View window as shown below.