One of the most widely used ways to share and download files in peer-to-peer transference is by using a torrent file . File extension torrent is basically a protocol for downloading archive of files that are typically URL of a file or group of files downloadable with a peer-to-peer (P2P) file sharing program. Downloading from the torrent file reduces the burden in the single server, as it is distributed to the whole network. The torrent file allows people downloading the same file to upload data to each other. Downloads are split among multiple nodes and the nodes then download the pieces from each other, which reduces the bandwidth used by the primary server and speeds up download times.
In other words, a file extension torrent is simply a pointer file to the location of parts of the real file on the Internet. The Torrent client software puts your computer into a peer-to-peer network that then collects the various parts of the real file using the torrent file as a guide. Meanwhile, your computer serves as a server to collect parts of other files and forward them to others while you are connected. While you download the archive to your computer, you are also helping to distribute it to other users. In essence, torrent files include instructions for a compatible P2P clients where to find the "tracker" for the downloaded file, hashed checksum that verifies for the client that it is actually downloading the correct file, the full size of the file and the filename of the file.
So, technically .torrent files can be downloaded in matter of seconds as they are very, very small files that simply contain some textual data about the file itself. But in a computer with a peer-to-peer compatible client installed in it, launching a torrent file typically starts a process where the compatible client first contacts the tracker described in the torrent file and if the tracker server is found and "seeds" (people sharing the file) are available, launches a download process of the file described in the torrent file.