Welcome to GTPlanet, and welcome to the tuning experience!
Maybe others have been slow to answer because this is really such a big question, and there is no right answer which applies to every driver/car/track/etc. Search around for general tuning guides to get a feel for what the different options do.
But just a quick bit of advice to get you pointed in the right direction:
Tranny: you're got the customizable gears on, go to the test track 1000m and look at your power curve. find where the power really starts to drop off as you go down the rpms. remember this number. now go set your gears. I usually set 1st as tall as possible, and then I try to get 2nd-5th to start at or near the rpms where power is still good. take a few test runs and see where the rpms are when you shift up, and go back to settings and make adjustments until you get it where you want it. final gear should be set so you're pretty much at redline in top gear when you hit 1000m.
Springs: depends on the track. go to a track and run test laps. set the springs high, then set them low, and watch how when they're high you get a very bumpy/skippy ride (on some tracks especially, and this is bad). when they're soft, you don't corner as well. in between you find a setting where you corner well and also you're not skipping and bouncing and losing tracking when the track gets rough. Honestly, I usually run it stock and if it's super bouncy I'll soften it a little, if it's not bouncy at all I'll tighten it a little, but otherwise I leave springs alone.
I usually set ride height lowest in front, maybe 4mm higher in back. Brakes maybe 16 front, 12 rear. Camber for FR usually 2.0 front and 0.8 rear. dampers i usually set front a notch above stock, leave rear setting alone, but in the case of fully professional I'll set rebound one point lower than bound for both front and rear. Stabilizers and toe I usually leave alone.
And all of this is because I'm kind of lazy and so even thinking about doing the work it takes to find the best settings gets me unmotivated, and these settings seems to do fine for me.
There are really some great guides out there, check the GT2 forum, and maybe the "guides" tab at the top of the page, too.
