Commercial drivers licenses are regulated and issued by individual states. The requirements vary slightly from state to state. For example. in California a Class C license lets you drive any two axle vehicle up to 26,000 GVWR (gross vehicle weight rating), a 3 axle vehicle up to 6,000, a housecar up to 40 feet. You must check the motor vehicle regulations in the state you are planning to obtain a license.
A Class D license permits a person to drive any single vehicle, provisionally, with weight restrictions. For example any vehicle not exceeding 26,000 pounds is allowed to be driven.
Anyone with a proper drivers license may operate the vehicle the license is for regardless of the number of passengers the vehicle may carry. For example a standard Class F license permits the holder to operate any light truck, passenger van, or passenger car, regardless of the passengers present in those vehicles.
A class a cdl license allows someone to drive a heavy vehicle with a gross vehicle weight (GVW) of 26,000 or more pounds. Example: 18 Wheeler
An International Driving License (IDL) is an identity document which permits its holder to drive a personal motor vehicle in any other country that recognizes the IDL.
You can't drive any class of vehicle that way. If you don't have the licence, or else a permit and an appropriately licenced driver with you, you can't drive it.
Whether a vehicle has air, hydraulic, or air-over-hydraulic brakes has zero determination on the class of license required to operate it.
Sixteen with permits, eighteen with drivers license.
If you don't have a CDL, you can't operate a commercial vehicle. You can't even so much as be in actual physical control of the vehicle (in the driver's seat with the motor running). Even if you possess a non-CDL Class A or B licence, this holds true - a non-CDL Class A/B only permits you to operate vehicles which fall under the exemptions for CDL requirements.
A license, a vehicle, and insurance.
There is no difference between a driver's license and a driving license; they refer to the same official document that permits an individual to operate a motor vehicle legally. The use of "driver's license" is more common in American English, while "driving license" is more common in British English.
Class A, both in the case of commercial and non-commercial licences permits the operator to drive combinations over 26,000 lbs. GVWR, in which the vehicle in tow is rated at greater than 10,000 lbs. A Class A CDL doesn't necessarily allow you to drive a tractor-trailer - if you don't road test on one, but rather, some other combination which falls within Class A CDL requirements (for example, Ford F650 and a trailer rated at over 10,000 lbs), you'll get an "8" restriction - No tractor-trailers.
An AZ license allows you to drive tractor-trailers and other large commercial vehicles, while a DZ license only permits you to drive straight trucks or other commercial vehicles with a gross vehicle weight rating over 11,000 kilograms. In essence, an AZ license covers a broader range of vehicles compared to a DZ license.