In recent experiments, you found out that the current on a current path must always be equal. Current can not disapear or spontaneously occur. This is a direct consequence of the Kirchhoff's Current Law. Therefore...
To measure current, the amperemeter must be connected in series in the current path!
In order not to influence the measurement results, an ideal amperemeter has no internal resistance.
What do you need to know when measuring the voltage...?