Downloading the zip for Raspbian from https://www.raspberrypi.org/downloads/raspbian/ is taking hours. There is also a small torrent file that can be downloaded. How can this be used to install Raspbian?
First go to the official download page for Raspbian.
Click the Download Torrent button, the torrent should start to download. The torrent file isn't particularly large so should download within a couple of seconds.
You will need a program like BitTorrent to use the torrent file. Once you have installed BitTorrent go to the download location of the Raspbian Torrent file. Right-click on the file and select to open it with BitTorrent.
You should be greeted with something like this:
The preset settings should work just fine, but feel free to change any of them to suit your needs. If you would like to know more about using BitTorrent this page will be useful to you.
Once the torrent is set running the .zip file for the Raspbian installation will start downloading:
Once the download has completed you will need to unzip the 2017-14-10-raspbian-jessie.zip folder. Inside the unzipped folder you will find a Disc Image File called 2017-14-10-raspbian-jessie.
This file is what gets written to your SD card. to write the Disc Image File to your SD card is going to require a program like Win32 Disk Imager. Once you have it installed, open it and you will see a window like this:
Click the little folder button and go to the file location of the un-zipped Raspbian Disc Image file and select the file. You will also need an SD card connected to your computer and the location of that can be set under the Device drop down menu.
Once you are happy that you have the Disc Image File and correct drive letter for the SD card selected you can press the write button. It will take a few minutes for Raspbian to be written to the SD card. Once a message pops up saying the write was successful you can safely remove the SD card from your computer.
The SD card is now ready to be used in a Raspberry Pi.
The small torrent file itself cannot be directly used to install Raspbian.
It is just another way to download the zip file to install Raspbian. In some cases, depending on the specific torrent's activity, it will be faster or slower than the direct download link you specified. But in the end, you'll get the same zip file.
To use the torrent file you'll need a torrent client application as explained in Darth Vader's answer. If you install your torrent client before downloading the torrent file, your browser should automatically open the torrent file with your torrent application when you download it.