The Konftel 50 sits inbetween your phone handset and the phone base. The incoming phone line still goes into your phone.
First, unplug the handset from the phone's base. Plug it into the port on the switchbox with the handset icon on top.
The other side of the switchbox has two ports. Take the short wire (Which is in the right-hand port if the handset connector is facing you) and plug it into your phone's base (The same jack you just unplugged the handset from).
Finally, plug the 10 foot included phone cable into the remaining jack (This is the red cord in the diagram). The other end of this cord goes into the only jack on the Konftel 50 unit, which is on the bottom. Next to that jack is a small circular hole, which is where the power cord plugs in. Once that is hooked up, the machine is ready to go.
Making a computer connection for internet applications is even easier. Find the included cable, which has a normal phone connector on one end and two colored 2.5 mm plugs on the other. Somewhere on your PC's case will be a line of 2.5mm jacks. They will probably be on the back, either in a horizontal line towards the bottom or in a line on the left side. Sometimes, though, the jacks are on the front of the machine, especially laptops.
Many PCs have color coded jacks, and if this is so, just match the plug and jack colors. If not, plug the green one into "Line Out" and the pink into "Microphone."