1. If I use a voltmeter and I measure a 4.5V battery, and I connect the COM cable to positive and Vohm cable to negative I get a negative number on the display. Is this normal? So it means there are n amount of electrons (negative sign) that still have to travel to the opposite side?
Understanding electricity is a lot simpler if you don't bring electrons into it quite yet.
Since batteries are electrochemical apparatuses, their internal physics involves electrolytes and ions. Let's talk in terms of abstract electric charge. The positive terminal of a battery emits positive charge, and the negative terminal sinks positive charge. Positive charge flows from higher potential to lower potential.
The two terminals are at a potential, which is the voltage given on the battery's packaging, and which enables it to act as a power source. Say, you have a new 1.5V battery. In that battery, the positive terminal is at +1.5V in relation to the negative terminal. Which, conversely, means that the negative terminal is at -1.5V in relation to the positive terminal.
2. I was reading that resistance reduce the voltage..here I had a doubt because I though it reduces the current. Could you clarify?
I = U/R - This is Ohm's law. The current across a resistor equals the voltage across the resistor, divided by the resistance.
If you place a 1 kOhm resistor in series with your 1.5V battery, the full potential of the battery will appear over the resistor. Therefore, the current will be 1.5V/1kOhm = 1.5mA.
Now, if you took ANOTHER 1kOhm resistor, and inserted it into the circuit in series (ie. battery - resistor - resistor - back to the battery), now the voltage of the battery appears across the two resistors. The current in the whole circuit will be 1.5V/(1kOhm+1kOhm) = 0.75mA. So yes, adding extra series resistance DID reduce the current flow.
The voltage drop (ie. the potential difference) between the "hot" terminal of the first resistor (connected to the + terminal of the battery), and the "cold" terminal of the second resistor (connected to the - terminal of the battery) is still 1.5V, as the battery keeps it that way. But if you took a measurement across the two terminals of only the FIRST resistor, you'd see a voltage difference of 0.75V!
Why? Because Ohm's law works in all combinations. U = R*I. So with a current of 0.75mA, the voltage across one resistor will be 1kOhm * 0.75mA = 0.75V! The voltage is divided across the two resistors, with each of them
dropping 0.75V, which adds up to the total 1.5V.
Though if you connected the two resistors in parallel, things will look significantly different.
BTW I don't know what kind of source you use to study some electronics, but I think you need better ones. The Electronics for Dummies book is pretty good for the basics, actually. There are also lots of good explanations on-line. And don't worry about electrons for now, they will just confuse you.