Re: what is voltage ?
This is hard to answer because I don't know your background. Voltage is a potential difference. Now, depending upon your background, that statement might not mean much. To think about potential difference, imagine a large sum of charges in one place, and a lesser amount of charges in another place. There is a difference between these two places ... a potential difference. If I connected the two places together with something that would allow the charges to move through it, I would have current flow, or moving charges. So, potential difference, or voltage, is the driving force for current flow.
As for current flow, Ohm's Law determines how much current can flow. V = IR, Voltage is equal to the current flow time the resistance. Rearranging shows that if the voltage is constant, then the resistance will determine how much current flows. Theoretically, if you connected the two clouds of charge with something that has no resistance, then an infinite amount of current would flow, and on the other extreme no current flows when the two clouds are not connected.
Now that you know what voltage is, with a few web searches you should be able to answer "what does 1 volt mean?" by yourself. Do a web search on "Electric Voltage".