It's not necessary to alter the car setups - of course you can do this and tailor the car to a particular track and conditions.
Personally I don't touch the setups and just race the cars on default setups.
Track temperature is important. I suggest picking a low powered car (e.g. Ford Escort RS1600 - Class Road G), then go to the track you know best with the date set to summer. Get to know how cars from different classes react on default settings.
As far as turning - you can't just mash the brakes like GTS - apply them gradually allowing time for weight transfer. Brake early - much earlier than some other games and use the weight transfer to load up the front tyres and initiate rotation of the car. Get back on the throttle early. With something like the Escort the first part of the turn is the brakes and a little steering, the completion of the turn is throttle and a little steering - most cars you will hardly turn the wheel if you have setup for the corner - slow in, fast out being very careful about positioning on the track
Are you on wheel or hand controller? If wheel I suggest all aids off including ABS and take your time to get to know the feel of a few cars. Good cars to start with are Ford Escort (Road G), Ginetta G40 and other low power front engine, rear drive cars.
Good luck and happy driving!