Getting started with the APi

I am trying to get started using the API, but am lost at all the getting started videos as none are making much sense - probably because I haven't coded fore so long.

What I am trying to achieve is to create folders and their sub folders within box.

The process being my windows app will pass two numbers to the program / api, the program checks within our Box system to see if the numbers exist as folders or not.

If they do, it then checks if a predefined folder structure (currently held within a xml file) exists below these two numbered folders.

If they do not exist the first number folder is created, then the second number folder is created as a subfolder, finally the folders laid out in the xml file are created. 

This app will be created in C#, winforms  - unless I need to look at another language to create it in.

Where do I get started?

Matt