Class A Class A Is a tractor or a truck pulling a trailer that is 10,000 lbs. or more with a combination weight of 26,001 lbs. or more. Also known as a combination vehicle. This is the most difficult because of the trailer. But someone who holds a Class A can also drive Class B.
Class B Class B Is a straight truck with no trailer, such as a dump truck or a bus that is over 26,000 lbs.  Someone with a Class B cannot drive a Class A. Class C

Class C Any vehicle under 26,001 lbs. with either a passenger endorsement or a hazmat endorsement. Class D Class D Is the license you should currently have to drive your car. Class C Class B Class A Class D