Hello and welcome to TSR!
Don't worry, you are not the only one who has difficulty grasping the concepts. Mainly because it's not easy to visualise what is going on.
There is a lot to take in and you have to go over it quite a few times before it all of it makes sense.
Think of a power supply. All work must have an energy source be that for lighting a lamp to pulling a train using an electric motor.
The power available from the source is transferred through the movement of electrons flowing in the conductors. Electrons repel other electrons so the push 'pressure' comes from the source and ripples around the circuit rather like how a bicycle chain transports energy from a riders legs to the road wheels.
Voltage is therefore defined as Joules/Coulomb. i.e. the energy available from the source that can be transferred for every Coulomb (quantity of electrons) of charge.
You can now see that if the voltage increases it means more energy for a given amount of charge (electrons) is available to do work.
1 volt = 1 Joule of energy for 1 Coulombs worth (given mass) of electrons.
Potential Difference:
When the electrons are forced to do work by say heating up a resistor, energy must be being used.
So the potential energy available at the entry to the resistor MUST be different to the potential energy left at the exit to the resistor because some of that potential was converted to actual heat energy in the resistor.
Can see where this is going?
Potential difference does exactly what is says on the tin: it's the amount of potential energy used up between two points in a circuit. (Rather like gravitational potential gets used up as a stone drops through the air.)
PD is measured in volts because its the same definition as voltage:
PD (volts) = Joules used per Coulomb of charge. V = E/Q
That's EXACTLY why the voltage drops (potential drops) around the circuit must equal the source voltage.
You should now see from the previous explanantion that in a parallel circuit, all parallel components have access to the same source of POTENTIAL energy because they are all simutaneously connected to it.
And since potential difference is the amount of energy used between two points, the pd across the parallel components is a measure of the energy used in ALL of those PARALLEL components SIMULTANEOUSLY.
The energy is shared because the limited quantity of electrons have to travel down different parallel paths but all join up again as they leave the parallel components. (Like water diverting around rocks in a river.)
Parallel components are connected to the same points in a circuit.
Series components are connected end to end. The first component uses up some of the potential energy available from the source. This leaves less energy avaiable for the next component which uses up more of the energy and so on.
So each component will use up energy and hence the potential difference across a series component is a measure of the energy used up in each INDIVIDUAL series component because its the only thing that electrons are flowing through in that part of the circuit.
Should now be expalianed above.
A
battery is a source of potential energy. So battery voltage means the amount of energy available per Coulombs worth of charge.
2 Volts means 2 Joules for every 1 Coulomb of charge is available.
3 Volts means 3 Joules for every 1 Coulomb of charge is available.
Lamps do not supply energy, they use it. A 3V lamp means that it is designed to work at optimal light output when supplied by a source of potential energy that is able to deliver 3 Joules per Coulomb of charge. (i.e. source =3V)
A 230V lamp works optimally when connected to an energy supply source capable of providing 230 Joules/Coulomb of charge.
I'm going to stop while you digest the previous information and see if you can answer the last two questions based on the explanations already given.
If you are still having difficulty, can I ask you to post a new thread as the answers are somewhat based in manufacturing practicalities rather than physics laws.
Thanks.