To help your understanding, I will explain further.
To measure current in a wire, you break the wire and connect the ammeter in series with the wire.
Ammeters usually measure small currents, say 1 milli-amp.
If there is 10 amps flowing in the wire, the meter will be destroyed.
So, we use a low value resistor to "shunt" most of the current past the meter, and just let a small curent flow in the meter.
When a current is flowing through the shunt, (or any other resistor), there will be a voltage developed across the shunt.
In the example you have, that voltage is being measured by the oscilloscope.
So, if you know the resistance of the shunt, and the voltage across it, you can use Ohms Law to calculate the current.
JimB