Ways of connecting bulbs
In series connection consumers are joined one after another along a single path: current passes through all the lamps in turn. If one goes out or is removed the circuit breaks and the rest go out too. The more lamps, the more the source voltage is shared and the dimmer each shines. In parallel connection one end of each consumer goes to point A and the other to point B; current branches and each lamp receives the full voltage of the source, so identical lamps shine equally brightly. One going out does not affect the others. In parallel the total current is the sum of the currents in the branches, so the battery drains faster. Lamps, sockets and appliances in our homes are wired in parallel: if one goes out the others keep working. Old festive light strings were in series, and one burnt-out bulb switched off the whole string. Safety: for experiments use only batteries up to 4.5 V; do not touch the lamps or sockets in your home.
Connection experiment: with a 4.5 V battery, two identical lamps (with holders), a switch and wires assemble first a series then a parallel circuit. Compare the brightness in both cases, then unscrew one lamp and see whether the other stays lit. Safety: assemble with the switch open; use only a battery; check that a lamp has not heated before unscrewing it; stay away from sockets and wires.