Resistance
Electrical resistance is a property of a material that impedes the flow of electric current. The unit of resistance is the ohm(Ω).
When a voltage of 1V is applied, the conductor's resistance that allows a current of 1A is 1Ω.
When the voltage is constant, the current flowing through the circuit is inversely proportional to the electrical resistance. In other words, when the electrical resistance becomes 2 times, 3 times, 4 times..., the current becomes 1/2, 1/3, 1/4... In this way, the current flowing intensity through the wire becomes smaller as the electrical resistance increases.
In parallel circuit,
The current splits up when it comes to a branch. The current in all the branches adds up to the current in the main part of the circuit.
If one bulb breaks, the bulbs in the other branch stay on.
If you add more bulbs, each bulb stays bright. It is easier for the electron to flow because there are more ways for the electrons to go.
In serial circuit,
The current is the same everywhere.
If one bulb breaks, all the others go off.
If you add more bulbs, they will be dimmer because it is harder for the electricity to get through - the resistance of the circuit is higher.