Resistance us a restriction to of the flow of electrons
It is measured in Ohms
If we add multiple devices in the circuit in series the resistance in the circuit will increase which makes it difficult for the electrons to flow and hence reducing the current in the circuit
In a series circuit the current everywhere is the same
In a parallel circuit the current will be divided between the devices connected in parallel
We can add resistors to our circuit to control how much current will flow through it
The excess current that is flowing through the resistor leaves the circuit in the form of heat