Delay is a time-based effect. The effect processor samples the original sound and replays it at a delayed time interval. You can set the time between original and delayed sound to create anything from an immediate "tiled room" room echo to a large "cave" type echo. The "Mix" control on the delay effect governs the level ratio between the original signal and the delayed one. When used with an acoustic guitar, delay approximates the effect of various acoustic environments. It works well with electric guitar too, but it really brings out the characteristic "jangling" of the acoustic guitar's sound.
Chorus is created by using a short delay effect. The original acoustic guitar signal passes through the effect processor normally. The processor samples the signal and allows it to pass almost immediately after the original. The gap between the original and delayed effect creates an ensemble effect, similar to two guitars playing at the same time. You can modulate the delay time and the intensity of the effect using the "Ratio" and "Level" dials on your chorus pedal. When used with an acoustic guitar, the chorus effect creates a gentle "wobbling" or "shimmering" sound that enhances the subtle nuances of the guitar strings.
Flange and phase function is a method similar to chorus, but have slightly different tonal characteristics. Where a chorus creates a "wobbly" sound, flange creates a more intense "fluttering" sound and phase creates a distinctive "sweeping" sound. The difference in sound is determined by the modulation parameters of the individual effect processor.
Reverb is similar to delay, but is more subtle. Where a delay effect emulates an echo, reverb emulates the persistence of the acoustic guitar's decay. The decay is the time it takes for a note to fade out. By prolonging the fade, the reverb pedal adds resonance and color to the already bright sound of an acoustic guitar.
This is a more subtle effect, used more for correction than enhancement. Compression limits the dynamic range of an audio signal. It boosts the quiet notes and cuts the quiet ones to bring the overall dynamic spectrum within a predetermined range. Compression is used to mitigate feedback problems when amplifying an acoustic guitar. Acoustic guitars are prone to feedback because of their hollow nature.