Regarding ur doubt abt the voltage and current, when u ll be completing the ckt u ll , of course be joining one or more voltage source, it is this voltage source/s which will be driving the current through the ckt. What is resistance? it is nothing but the property of the element to resist the flow of charges through it, right? So when ever current flows through it there is a corresponding voltage drop (V=IR).
i hope this solves ur problem
1. Any small or big closed ntw can be called electrical ckt, where as electrical system usually consists of many ckts.
e.g. a bulb connected to a battery and the whole power grid.
2. In series ckt current flowing through various components is equal. The voltage is always measured between 2 pts. and whenever current flows through a resistor there is a voltage drop. So yeah when u ll observe a drop in voltage in the process from (i) to (iii).
there ll be voltage drop but the current ll remain same.