A Flanger is not too dissimilar to a Phaser, but can be much wetter sounding. This where you get that wonderful sweeping ripple. Because you have two opposite phases of the same note sitting within each other, a notch is created where they cancel each other out and then these notches are swept along a range of the frequency band.
One of those has its phase shifted and then they are laid on top of each other before exiting the pedal. As your signal goes into the pedal, it is instantly split into two. This creates movement, modulation, and if you go too far, chronic seasickness.
