i need info about nitro gas rc cars?

when it says scale of 1/10 speed or 1/16 speed or 2 speed what does it mean.

This is a very general question. The RC car fuel is very large. The scale refers to what fraction of the size to the original vehicle it is. So a 1/5 scale would be bigger than a 1/24 scale. The 1/8 and 1/10 scales seem to be the most popular for nitro-powered vehicles respectively. 2-speed means that the car can switch gear ratios either through the spur gear, clutch bell, or by a transmission. Usually a 2-speed is not recommended in an off-road application but is more commonly used in on-road cars. A 2-speed will generally give teh car more acceleration and some more top speed.
You can choose from from monster trucks, buggies, truggies, stadium truck, cars, rock crawlers, or even the new stock cars. These vehicles are powered by glow fuel called nitro which is a mixture of nitro-methane, methanol (basically what you get out of the gas pump), and oil.