What is a parallel and a series circuit?

The terms "parallel" and "series" refer to the two different ways in which the elements of an electrical circuit can be connected. The elements of the circuit could be light bulbs or household appliances, or electronic devices such as resistors, capacitors, or inductors.
In a series circuit the elements are connected to each other in a row, one after another (please see the reference links for the illustration). Only one end of the first element in this row is connected to the positive terminal of a battery, and only one end of the last element is connected to the negative terminal. Thus, all elements of a series circuit have the same current going through them (there is no other way for the current to go), but the voltage supplied by the battery is split up between the elements proportionally to their resistances.
In a parallel circuit each element has both of its ends connected to the battery - one to the positive terminal, and the other to the negative terminal. (Again, please see the reference links for the illustration.) Therefore, all elements of a parallel circuit have the same voltage supplied to them by the battery. When a household appliance is plugged into an electrical outlet, it is connected in parallel to the external electrical circuit, which is connected to the generator. The current going through the battery or the voltage source splits up between all branches of the parallel circuit, in such a way that the elements with less resistance have more current.
 
https://www.allaboutcircuits.com/textbook/direct-current/chpt-5/what-are-series-and-parallel-circuits/

https://www.physicsclassroom.com/class/circuits/Lesson-4/Two-Types-of-Connections