You can now import the feeds you had in other readers such as Google Reader into WP RSS Aggregator. You can thus easily use the plugin to create your own self-hosted aggregator.
The first step is thus that of entering your feed sources. To do this, head over to the Tools > Import page.
Click on the Choose File button, and select the OPML (.xml) file you have on your computer.
Finally click the Upload file and import button and the feed sources will be imported into WP RSS Aggregator.