To measure the current flowing through a component in a circuit, you must connect the ammeter in series with it. Remember, electric current is measured in amperes, or amps for short.
Now in a series circuit, all the electrical components are connected by wires in one loop. So there's only one route for the current to flow. Now electrons pass through all of the components in ...
Can you do the same thing with electronic circuits ... if you set the total current to, say, four times the base current, then R2 will get three times the base current through it.