Upvote:3
Not really sure what your question is asking, but if it is around just the passport uploading bit then that is easy - the company will tell you to upload a scan of particular pages from your passport (often the personal identification and relevant visa pages) - but some companies just want you to tell them the key details.
They will also tell you exactly how to do that (some have a web application, some want the details emailed)
As to why - that's so they know who is travelling, and can validate passenger details.