It works like this: someone downloaded a movie from your computer, and now that file is available for download from two sources. And so on in ascending order. That is, those who have downloaded it also become "donors" and distributors of this material. Special programs determine who has access to the desired file and saw from it for download. Thus, the load on the computers of the distributors becomes minimal. The more people share files, the higher the download speed. By the way I recommend you torrent https://thenewpiratebay.org/, very reliable.