In a series circuit, it is a single loop end to end. One component of the circuit being removed can affect the rest of the circuit.
A parallel circuit has more than one loop, and if one of the loops is broken, the circuit is still complete.
In a series circuit, the voltage is shared between components, and the voltage of each component adds up to the total voltage
In series circuits, current is the same everywhere and the same current passes through the whole of the circuit, and is based on the voltage and resistance of the circuit
In a series circuit, the total resistance is just the sum of the resistance of the resistors in the circuit. If the resistors are identical, voltage is evenly spread across the resistors
In a parallel circuit, the voltage is the same across each component.
In a parallel circuit, the total current is the sum of the currents in each branch.
In parallel circuits, total resistance decreases as the number of resistors parallel to eachother increases