An ammeter is the meter used to measure the current in a component. Current is measured in amps (A). In circuit diagrams an ammeter is drawn as a circle containing the letter A.
An ammeter must be connected in series with the component. This means it is placed in the same loop of the circuit, one after the other, so that all the current through the component also passes through the ammeter. To do this you break the circuit next to the component and put the ammeter in the gap.
A good ammeter has a very low resistance, so it does not change the current it is measuring. This is why it is never connected in parallel across a component. A voltmeter is the opposite: it is connected in parallel. In a series loop the current is the same everywhere, so an ammeter placed anywhere in the loop gives the same reading. A small lamp might carry a current of about 0.4 A.
