Series circuits

In a SERIES circuit the bulbs components are connected one after the other.
In this type of circuit the current is the SAME AT ALL POINTS IN THE CIRCUIT.

Parallel circuit

In a PARALLEL circuit the components are connected side by side.

The current SPLITS AT THE JUNCTIONS (S) some going one way and some the other. If the bulbs are exactly the same then the same current will flow through each bulb.
If one bulb has a higher resistance than the other then less current will flow through that bulb.

If the batteries and bulbs in both circuits are the same then:

(a) the bulbs in the parallel circuit will be brighter than those in the series circuit

(b) the battery in the parallel circuit will run down more quickly than the one in the series circuit