If you have decided to pursue a career in aviation, a commercial certificate is the minimum certificate required to be able to work for a company and get paid for your work. With such credential you will be able to fly for a regional airline as a first officer, for a part 135 freighter or a charter outfit as both a captain or as a first officer ; or for any part 91 company like pipeline or traffic watch or skydiving operations. This is providing you meet the minimum hours required for the position set forth by the FAA specific to the type of operation and by the company itself. Before you start the training, you will have to decide if you want to acquire your multi-engine rating at the same time or start with your single engine commercial first then do your add-on multi-engine commercial later on. Doing your initial commercial in a multi-engine airplane will increase the costs but provide you with significantly more multi time, which is important to get hired, especially lately. Regardless, to be a commercial pilot in both types of airplanes, you will have to go thru specific courses and two distinct FAA check rides. You will acquire advanced weather, navigation and systems knowledge, especially about multi-engines. In the airplanes you will learn new maneuvers such as chandelles or steep spirals and work on already known ones like stalls to better your stick skills. In the multi-engines airplane, you will learn about engine failures during takeoff and in flight, and their various effects on the airplane’s performances. You will also work on cross country during day and night time. Once again you will have to pass a written test ( valid for both single engine and multi-engines airplanes ), and as usual the two check rides will include an in depth oral examination and practical test with more stringent standards, like +/- 50 ft from assigned altitude. Good luck !