Complex sentence: Commercial driver's license training (or CDL training) is a specialized instructional program or course designed to prepare a student to obtain a commercial driver's license (CDL), which is required for a career as a truck driver.
Split into simpler sentences: Commercial driver's license training (or CDL training) is a specialized instructional program or course designed to prepare a student to obtain a commercial driver's license (CDL). A CDL is required for a career as a truck driver.