No you remove the device's battery and place that into the charger which in turn is plugged into USB via your wall charger.
Also it's probably not a bad idea to have another battery so that you can cycle one so that you can still use your phone whilst charging your other battery.
I apologise I posted a link to the wrong battery type for your phone, this is the one you need:
Amazon.com: Blackberry OEM Mini External Battery Charger for 7100 8100 8300 8700 8800 series - ASY-12738-001: Cell Phones & Accessories