You must be 18 years old and a licensed driver to apply for a commercial driver's license (CDL). Most states don't require any training prior to applying for a CDL, but training is useful. A commercial driving school, more popularly known as a "truck driving school," will teach and train you to pass state-required CDL tests. The total time required to obtain a CDL license depends on you and your educational needs. With training, it could take four to six weeks to get your CDL. Without training, it could take as little as one week.

Take a commercial driver's course. Most states don't require the completion of a commercial driver's course to apply for a CDL, but this type of course will prepare you for the CDL tests that are required. Training typically lasts three to four weeks.

Read your state's commercial driver's license handbook. Most states have this document available at their department of motor vehicles (DMV), or online at the DMV's website. You will be tested on the handbook's information.

Go to your local state DMV. Bring your state-issued driver's license and social security card.

Complete a CDL application. Enter your full name and address, Social Security number and date of birth, and check the class of CDL you are applying for. There are A, B and C classes. Each class allows you to drive a different type of vehicle. Class A license holders can drive a vehicle with a combined truck-trailer weight of 26,001 pounds or more, and the towed trailer can be over 10,000 pounds. Class B license holders can drive a vehicle that is 26,001 pounds or more, but the towed trailer can't exceed 10,000 pounds. Class C license holders can drive vehicles that do not exceed 26,001 pounds, and tow trailers that exceed or are under 10,000 pounds, provided the combined truck-trailer weight does not exceed 26,001 pounds. There are also endorsements required to drive a vehicle that has passengers such as a bus, or to haul materials that are hazardous.

Complete the CDL written test. The number of written tests required depends on the license class and endorsements that you're applying for. You are required to inspect a vehicle similar to the one you are driving, and successfully complete a written test on CDL regulations and driving laws. There is a fee for the written test. A permit is issued to successful test applicants.

Complete a CDL skills test. Some states require that this test be taken within six months of the date your permit is issued. This exam tests your actual driving skills. There is a fee for the skills test. A CDL license with the proper endorsement is issued to applicants who successfully pass the skills test.