Send (or Util-Send) provides the send/return functionality found in most mixers but for a single stereo channel. Just connect you audio to the inputs and take from the outputs. Connect your effect from the send jacks and connect it back in the return jacks.
Documentation
Blend: controls the mix between the unprocessed and processed signals. Includes an input modulation with attenuverter.
Send (jacks): provides the audio signal to connect to you audio processor.
Return (jacks): inputs of the processed signal.
Output (jacks): the mixed audio signal.
Input (jacks): inputs the unprocessed audio signal.