1) that's Release, not relay
2) the ADSR on a filter is used to open/raise the filter cutoff frequency, making the sound brighter/more full of higher harmonic content
3) the Sustain part of the filter is a constant amplitude or constant level, so causes the filter tostay open at a particular point, the higher the value the higher the point
4) Attack is a rise time, Decay is falling off time to the Sustain level, and Release is a dying away (literally a decay) time closing the filter again.