Formula Trainers is a semi-fictional category that is likely based on Formula Ford. The category consists of a single car with two configurations, raced in two different classes.
This junior open wheel single seater doesn't immediately make sense if you compare it to fast formula cars. But the reason it can be considered a trainer car is, because it teaches you car control without any help from aerodynamics or state-of-the-art mechanical grip.
Fundamentally the car is the same as any modern formula: mid-engined, rear wheel drive, lightweight and stiff. What it lacks is rear downforce that would stabilise it at high speeds. It also has an open differential which means that the rear axle has no added mechanical stabilising effect off throttle which is common in most formula cars.
The end result is a sensitive car that you have to drive with care. You can't lift throttle too quickly when turning in or the car will start spinning from weight transferring to the front. It also reacts to bumps and crests so you have to stay alert.
Like with the Formula Vee, once you get used to the car you can try and start using its sensitivity to your advantage. Some corners can be taken faster by turning in quickly with the help of this built-in ability to rotate.
Ultimately you don't drive an F3 or F1 car the same way. But if you can tame the Trainer, you can adjust to a more aggressive setup with high aero formulas and rely less on rear downforce to keep you safe.
Trainer Advanced vs Simple
The simple trainer class has simple analog gauges and semi slick tires. It's more forgiving to drive thanks to its progressive tire grip.
The advanced trainer has an LCD screen instead of simple gauges. It also uses full slicks so grip is less progressive. It will feel more twitchy initially. But there's more overall grip available so it's faster around the same track than the simple trainer.