what programms are needed to download torrents. My pc tells me canont find source file.

There are a lot of torrent programs around. Too numerous to name them all here. There are those that are only torrent programs & these are the best. Then there's those that run on multiple networks like LimeWire, ShareAza, etc.
My suggestion would be to aim for either Vuse: Azureus, now called Vuze : Bittorrent Client _ OR _ uTorrent: Torrent - a (very) tiny BitTorrent client