Connect the microphone to your mixer, then the mixer to your i7100. The outputs of the i7100 can then be connected to an amp and speakers (or you may also like to connect the i7100 to a channel insert, if its easier).
The easiest way to set up the i7100 is to recall preset 6, which ensures all filters are set to automatic. You do this by turning the program control until the Preset LED lights up. Press the preset control and turn again until 6 appears on the display. Pushing the program control again will select this preset number.
This will catch feedback much easier when the person speaking into the microphone is moving constantly. If not enough feedback is being caught, you may also adjust the threshold to help combat this.