I like to use Synaptic to install software. To start it, type: Alt-F2 to bring up the run dialog. Then type gksu synaptic. gksu is the GNOME super user do application. It lets you run graphical applications with administrative privileges. Type your password into its dialog and wait for synaptic to start. In the quick filter or search dialog type ktorrent. No need to hit enter. The list will be immediately filtered if you use the quick filter box. Click the check box next to ktorrent and then the apply button on the toolbar.
Alternatively, open a terminal and type sudo apt-get install ktorrent. Type your password and perhaps enter to accept installing additional packages if prompted.