If it is anything like my Pascar/Amprobe type, you would have a Transmittier - which gets connected to the Circuit to be traced, and a Receiver - which is placed on the Circuit Breaker, or wire, in a Panel.
Transmittier requires Power from either the Circuit in question ("Live" testing), or a Battery (Ringing Out "Dead" stuff).
Transmitter should pulse a tone on the Circuit, which is picked up by the Receiver at the Panel.
Place Receiver directly on the breaker or wire, at a "Right Angle" to the current flow.
The "Pick-up" end should be apparent, so place it against the breaker/wire, making sure the receiver is positioned so the widest part of the pick-up is at a 90° angle to the direction of flow.
Hunt around until you get a strong and stable signal, then throw the breaker off.
Best to test non critical circuits for a few hours / days first, so you can get the feel for the tester. Takes a little time to get used to how they work under different conditions, so you can accurately find the right circuit.