Current: it’s the flow of electrons in a circuit. The higher the current the faster it is. lower the current the slower it is.
Voltage: it’s how much the circuit current has.
as you see that the series circuit is brighter than the parallel circuit, it’s because the current on the parallel circuit is slower then the one in the series circuit.
The current is slower in the parallel circuit then the series circuit area because in parallel circuit, the current takes different paths around the circuit to light up 2 or more bulb so it has to split equally to cross each different patch, while the series circuit, it only has 1 path and so the current isn’t split or shared across different path.