There are two kinds of electrical circuits, series and parallel. Components that are connected one after another on the same loop of the circuit are connected in series. If one lamp were to break in a series circuit, all the lamps would stop working so it's hard to tell where the source of the problem is.
Components that are connected on separate loops are connected in parallel. If one lamp breaks, the other lamp will still light which makes it a lot easier to fix.
When two or more components are connected in series, the same current flows through each component. But the voltage is shared through the components. This means that if you add together the voltages across each component connected in series, the total equals the voltage of the power supply.
In a parallel circuit however, the voltage stays the same throughout the circuit but the current gets divided up through the components.
To measure the current of a particular position in a circuit, an ammeter can be placed in series. So in this case A1 will have the same amps flowing through it as A2. In a parallel circuit however A1 will have more amps than A2.
To measure the voltage, a voltmeter must be fitted in parallel to the circuit. In this case, V1 will have half the voltage as V2. But in the parallel circuit, V1 and V2 will have exactly the same voltage passing through them.