Why do we have more than one resistor in a circuit?
The circuit may require different levels of current or voltage at different points. Consider a circuit that causes a led and a ring when a switch is raised.
the led will need a current limited to a certain level to avoid damaging the device, so the resistance will be added to the path of the circuit after the led and before the earth.
the buzzer may have a different current and a different value of resistance will be added to this circuit.
Also, in logic circuits, the resistors are used to increase or decrease a voltage to a valid level for that logic circuit, ensuring that the circuit has valid logic levels in both states.
A circuit consisting of a power source and a single resistor can only perform the function of converting electrical energy into heat.
This is useful if you are cold or want to cook. but you will want a way to control it. a simple switch to turn it on or off is nice. you may want more or less heat; having two or more resistors in different combinations in series and in parallel can solve this problem.
maybe some kind of overheating protection could prevent your house from burning. Add a microprocessor and some control circuits.
After a while, you may come to the modern electric stove. but there are many more things going on there in addition to the unique resistance with which we started.
So, to properly design this stove so that it is safe and effective, you must first know the supply voltage and the amount of heat required.
From these parameters can be deduced the combinations of series and / or parallel resistors which will work correctly.
We can leave the control circuits to be imagined a little later in your studies.