Need Math help please TF E proc!

I've been playing ADC TF and I'm not sure how my E reacts with my item build. Build:Guinsoo's>BezerkerGreaves>BotRK>Hurricane>LDR>IE/HextechGunblade/GA Explanation: Hurricane bolts help stack E so every 3 targets hit means 3 stacks. But how does Guinsoo's help? I know Guinsoo's at full stack does some magical thing every 2nd AA, but unclear how it works. Also how does Guinsoo's help BotRK stacks too if you can clarify this for me?