Answer:
In parallel circuits all components have the same voltage. In series circuits all components have the same current.
Explanation:
Voltage in a circuit is akin to pressure in water, while current is akin to flow in water.
Voltage and current are related to resistance by Ohm's law:
Where:
V: voltage
I: current
R: resistance
In a parallel circuit all the terminals of one side of the devices are connected together. This is known as a node. Nodes have a certain voltage. Devices connected in parallel will have one node on each side, and each node will have it's own voltage. Current will flow through each component independently depending on their resistance, so it is not the same for all of them.
In a series circuit components are connected one after the other, the current that flows through one must continue and flow through the next, so they all have the same current. But since they might have different resistances they might have different voltage differences between their terminals.
Parallel connection is useful when you have devices that require a specific voltage, such as household appliances. All wall power outlets are connected in parallel.
Series connection is useful when you want to control current. When you use a LED you must be careful not to apply an overcurrent, so a series resistor is commonly used to limit the current.