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