It is like other P2Ps, you download from other users and everytime you click on a BitTorrent download link, you also send to other users the data of the files you have in your computer. The more you upload, the more you download.
But it is not fully like other P2Ps, in the case of BitTorrent, you will not find any contact list, chat or anything like that, You will only have a main window where the files you are uploading/downloading are shown. If you want to download something, you will not have any search button, you will have to click on the BitTorrent link placed in any web and the program will start your downloading and it will be shown on screen automatically.
It is very easy to use, you only have to install it (a few seconds) and then, when you click on a BitTorrent download link, the program will start automatically. Of course it allows you to stop and resume the downloads.