2014 370z automatic transmission - manual mode

gpx123

Hey guys, got a 370z with automatic transmission and you know how when you move the gear stick to the left it goes to a sort of manual transmission not sure what its called think its called s-tronic or something like that?

But my question is how do you know when to down shift using the paddles? I've never driven a manual car in my life so this the closest I gotten I guess to it lol, but ok so I understand when you hear the motor at its peak you upshift but how do you downshift properly. Cause I feel like I'm doing it wrong, like when I start going slower and lets say I'm on 4 gear, I'll downshift when the speedometer seems to be like around the 2 and it feels weird cause the motor makes a loud noise and the speedometer arrow moves way to the right

any help appreciated : )