You need to set the “Source Module” field of the aggregator to where the bundles are coming from. This is usually an Iterator module, but can also be a search/list/repeater module, or even your RSS module.
For more information, please refer to the Make Academy.
I highly recommend doing the Make Academy as this is basic scenario flow.
Hope this helps! Let me know if there are any further questions or issues.
— @samliew
P.S.: Investing some effort into the Make Academy will save you lots of time and frustration using Make.