ya it's a two step process
first download the torrent file, which you already did.
then get a client like the above recommondation. Also Transmission and Azureus (props janey😛 ) are good ones.
You'll need to open a port in your firewall, which is located @ syst prefs>sharing>firewall>add a port.
a good default port # is 6881
and providing the torrent you Downloaded has seeders, you should be good to go.
Open the client, file>open...find your torrent file.
Go nuts.😀