Media picker upload file API call sequence



Hi, I would like to know if there is any documentation on using media picker to upload files? Doc here have little info on what APIs are expected to be implemented on server side to upload files. There are various API calls to upload files e.g. /upload/createWithFiles, /chunk/probe, /chunk/, /upload//chunks and /file/upload. I could not find in docs what are request params and expected responses for these APIs.
Can someone please explain these APIs or point to the doc somewhere?