ok i understand the kv rating and using it to get the motors rpm. what i'm
whating to learn hear is about the turns of the motor; 10.5t as an example.
how is it used in determining which motor to use for 1/10 scale or 1/8 scale?

The turns typically dont mean much, except that between different manufacturers they will all be pretty close in Kv for a given amount of turns. Most people just have a pretty good understanding that a certain amount of turns will be in a general range of Kv, therefore giving you the best option for your car or truck.
Typically the best truck drivers can use down to about 7.5T
The best touring car drivers can go as low as 1.5T since the car can put down more power
8th scale generally goes by Kv only