The API functions as a middle man between you (a developer) and the application. APIs were designed around the concept that you don't want people having to play with or dig through code to do what they want, but instead leave them access protocols for everything they could need. The API functions like a gatekeeper, it gives you a list of individual things you can do. APIs are also designed to be minimalist, so if you want to call a car, and all the parts to a car exist in the system, you're expected to call these parts and build the car yourself.

This is where the wrapper comes in as is what makes it easier for you to combine these rules with one call. If I wanted to build a car with no wrapper, I'd need to call all the individual parts with each call, save them somewhere and then start putting them together. With the wrapper, I can call all these parts within the same call, thus having them available to me to process all within the same instance.