Download a BitTorrent client application, like BitSpirit. Then install it just as you install any other software. Now when it's installed go to or, the latter being better and search for the software you want. Now I'm talking about btjunkie. The other one is similar. There will be many results. Note that new and more popular softwares will be available for faster as more people download them. When the results are shown the topmost wil have the highest speed. It's sorted in decreasing order of speed. On the left of every name there'll be a 'down' arrow and a '+' symbol. The down arrow is the button to download the torrent, not the file. The torrent is only a link to the file (It's about 10-30 KB). So you need to download or open that file with BitSpirit. Click on that arrow. Click on open or download the .torrent file and open it using BitSpirit (the first is easier).
Now the download has begun. It'll not start download at high speed all of a sudden. It'll take time to find other computers downloading the file. Now before you download let me explain what others are there in the results page. Next there is a + sign. When you click on it, the files that it has will be shown. In this way you can check if it's the one you want. On some names, it'll be written 100% fast download, but don't think it's always true. Now there will be categories written like video, audio etc. If unsorted is shown, then it could be any. You could use your common sense to recognise what it is, by seeing the name and size. Then there'll be number of seeds and peers. Seeds are the number of people giving (uploading) the file and peers are the number of people downloading the file. Then there's health (speed of the download). No need to mind that much. Just check number of seeds and peers. When you've started the download in the BitSpirit window, there'll be a 'down arrow (seed/peer)'. It's the download speed. As I told you the speed will increase.
One last thing to know is download only selected files. That is for example, if there's a album for download, you need only one of those songs. As I told you above, you can check if your wanted song is there in that album by clicking on the plus sign. Now in order to download only a particular file from the torrent. Download or open it with BitSpirit. There will be a small window shown. In 'Save to:' field, you can enter the location where you want to save the file to. Then on the 'File Options' tab you can select the files you want to download and click on 'OK'. In case you you forgot to select only the files you want, after the download has begun also, you can include or exclude any file. In order to do that, single-click on the job and below there'll be many tabs vertically. The second-last tab is the file options. In that you can set file priority for each file which is set to normal by default. Right click on a file and go to Set File Priority and set it to Do Not Download to exclude and for the ones you've accidentally excluded set it to Normal or some other priority as per requirement. Single click on a job an there'll be buttons on top - Start, Pause and Stop which are self-explanatory. After much time the down green arrow which is at the left side of the name in BitSpirit during download may change to a orange up arrow. It means that the download has been completed and it's now being uploaded. Ofcourse you can stop uploading but better do upload as much as you can.

All this may sound complicated but it's a breeze.