How to use Owncloud's APIs on a simple web application

Hello, i am a student and i have a project which is called personal cloud storage with raspberry pi. i already installed Owncloud and it works fine, but my supervisor asked me to develop a simple Owncloud web application that can do simple operations such as uploads,downloads and list the contents. the problem is that i am not good at programming and i don't know how to use API's, so could you help me how to build a simple one? i just need basic steps. and i'll be very thankful if you could help me, thanks again.