To select a datasourceDatasource, hover over the datablock Datablock header and click the icon.
To
select a datasource for a drillthrough datablock, hover over the datablock header and click the iconUse the "From Measure" to select the desired measures for your Datablock.
If you have an existing report that contains the measures desired, you may use the "Select Report" drop down menu select an existing report from your list.
Some Datablocks, such as the Drillthrough Datablock, require that you click the icon to access the Datasource.