fpiro07:
Hello everyone, I'm a complete newbie to the electronic world so I have some very basilar questions.
- What lights a LED up? Voltage or current?
To be pedantic: neither, carrier recombination lights it up. Both voltage and current are needed to cause forward conduction which leads
to more carriers in the pn-junction to recombine.
- What does a resistor limit? Voltage or current? I mean, if I don't put a resistor in my circuit the LED bursts down: why? Too much volts or amperes?
Resistor relates current to the applied voltage - higher voltage will drive more current, the only limit is when it burns up.
- What remains constant in a circuit? Voltage or current? I mean, what is the same at the start and at the end of a circuit? Volts or amperes?
I think you mean current - assuming certain things (such as its not a transmitting antenna), the current is everywhere the
same around a circuit. This isn't really true, since if parts of the circuit are changing their voltage some charge is used
to charge that part up, but for most practical circuits that aren't antennas it holds well.
- How should I put resistors when I have more than one LED?
One per LED to limit current individually (unless they are in series which means they all have same current
- How should I put resistors when I have series or parallel circuits?
That's a meaningless question - what are you trying to achieve? All non-trivial circuits have series and parallel elements.