Hi.
It would help if you mentioned which transmitter you have.
To keep it simple the end point ajustment limits the steering or throttle. With a standard radio and server most of my kits need the steering end points limited (turned down) otherwise the servo trys to apply too much steering. To be clear by too much i mean some part of the steering mechanism jams against some other part of the kit, this puts a strain on the servo which will eventually damage it, it may also deform parts of your kit and basically makes for an unhappy, poorly handling car.
You should have two end points for each channel, they allow you to adjust the left limit, right limit on the steering channel and the throttle, brake limits on the throttle channel.
Dual rate only applies to the steering channel, you can think of it as steering sensitivity.
A good starting point is to set the throttle end points to 100% and then forget about them.
For the steering I would also suggest setting them at 100% and then turn your dual rate down to 50%. Now turn your steering all the way left and check that no part of the steering mechanism is catching against any other part of the kit, then turn all the way to the right and make sure nothing catches. If this works add another 5 or 10% to the dual rate, keep adding and checking until you get to a point where any part of the steering mechanism catches any other part of the kit. You now have too much steering so back off the dual rate a little and you are now set and can forget that end points and dual rates ever existed.
What you have now setup is the full range of steering that your kit allows. Whatever your dual rate is set at now, remember it and dont go above this setting.
As I mentioned before dual rate is like steering sensitivity, I often have turn mine down for my kit maximum which makes my cars less twitchy, all my cars are grip cars so I cant say whether a lower dual rate will make a drifter easier to control.
With the budget equipment I use I normally have to adjust my steering trim a little to get the car to run straight again after adjusting the dual rate, dont worry if yours is like this.
I will leave it to someone else to explain that you should reprogram your speed controller if you have adjusted your throttle end points.
I hope this will help you to get a reasonable set up for your steering,
Duane