A simple circuit consists of a resistor, a battery, and connecting wires.

How must an ammeter be connected in a circuit to correctly read the current?

The ammeter must be connected in the series to read the current correctly. Ammeter has very low resistance If it is connected in parallel across any load then all current in circuit will choose lower resistive path (i.e ammeter) which will cause the circuit to be damaged. Hence it is used in series. Also the current in the series is always same.