How to upload files to box using android API

Question

How do I upload a file to a box account using the android API on android studio? So far I have done:

BoxConfig.CLIENT_ID = "ID"; 
BoxConfig.CLIENT_SECRET = "Secret Key";
BoxConfig.REDIRECT_URL = "ReDirect";
BoxSession session = new BoxSession(textUpload.this);
session.authenticate();

Now I'm trying to figure out how to upload a file that is already on the android device to box. How would I go about doing it?