In a series circuit, the same current flows through each part of the circuit. This means that we can measure the current at any point within the circuit and it will be the same as any other point in the circuit.
In the example circuit, we know the total voltage (9 volts) and we know the total resistance (550 ohms) therefore we can calculate the current of the circuit using Ohm's law, where I=V/R. This formula would give us a current of 9 volts/550 ohms or 0.0164 amps (16.4 milliamps).
Now let's look at the properties of a parallel circuit.