Difference between series and parallel circuits:
In circuits, two or more elements are in series if they exclusively share a single node and consequently carry the same current. On the other hand, two or more elements are in parallel if they are connected to the same two nodes and consequently have the same voltage across them.
We know that a node is the point of connection between two or more branches and a branch represents a single element such as a voltage source or a resistor or other elements.
In the figures below there are the representations of this type of circuits.
Example of when I would use them:
*Lighting systems, such as in a house or on a Christmas tree, often consistof N lamps connected either in parallel or in series,
*These type of circuits find continual applications in electronics, communications, and control systems.
*Lawnmowers have two switches in series with each other. Therefore, both switches need to be pressed before the mower will turn on.