TheWavMan breaks down attack and release by pushing both controls to their extremes so the effect is immediately audible.
A slow attack lets transients punch through for an aggressive, bold character; a fast attack smooths them out for a silky, controlled feel.
A fast release brings aggression back because the compressor keeps cycling, while a slow release holds the gain reduction longer for a smoother sound.
He then dials in the settings against the full track rather than the soloed vocal. For this melodic vocal, that means a fast-but-not-fastest attack (enough transient for presence without sounding abrupt) and a medium release (smooth but not over-compressed). The transferable rule: match the attack and release character to what the vocal is doing melodically, and always judge the result inside the mix.