Hi parsky1,
The dry sound first goes through delay A, which gets sent to the output. Delay B waits for the sound coming out of delay A and adds its own delay. So, for example, if delay A is set to 200 ms and delay B is set to 100 ms, you will hear your dry sound, then the sound again at 200 ms (delay A), then a third time at 300 ms (delay A + B). In mono, they both come out of the same channel; in stereo, they come out of alternating channels.