This question actually shows that do you not have a basic understanding of electronics, at least not on a conceptual level. Stop researching practical electronics, and electrical components like LEDs and resistors for a while. Instead start by googling Kirchhoff's laws, and read everything you can find about them until you have an eureka moment. Then do the same with Ohm's law.

Have you heard about, say... a voltage divider?

If you had a basic understanding of electronics, you would already have an answer to your questions. The things you ask are very basic indeed. Resistors don't "use up" current, nor do they "use up" voltage. Start some place besides youtube. Find a good written explanation with drawings and diagrams. Get yourself a voltmeter and an ammeter then build some simple circuits and make measurememts. Read up on Ohm's law, and relate that to your experiments.

So many questions! I suggest going to YouTube and searching "how do resistors work" followed by "how do LEDs work."

The simplest way to answer your own question is to learn about few common basic circuits and see if you can think on how to implement these without resistors. Eventually you will come to conclusion that you can't.

Yeah, so you have some practical knowledge about how to use electrical compononts, while your question is clearly about getting a deeper understanding of circuits as a whole, and what makes them tick. Hence my advice. Good luck!

Based on these comments, it looks like this SE community is pretty savage... Not sure why you all are so discouraging.

@maxathousand I find a lot of people get viscous when the Dunning-Kreuger Effet shows up. In this case, the questions are those which are answered in the first quarter of any introductory course on electronics (other than #3, which is actually decently complicated to answer). So the real answer is that the OP has reached a wall in their understanding, and is likely going to have to unlearn some things in order to learn how to do things in the way everyone else approaches them. It's an interesting challenge to convey...

... that without being savage and harsh. It's the skill of a true teacher something few on the internet have (including myself).

@AlmostDone: I specifically recommend NOT using youtube. A beginner is in no position to filter out the incorrect or misleading rubbish that you will find there. It is also very dufficult to produce a good video lecture - to the point that it is almost guaranteed that you won't find a good one produced by amateurs. It is also dfficult to flip back and forth and compare your circuit, the original diagram, the calculations, and the explanation of what the circuit does and how it works, and the troubleshooting tips that you will need to actually get the thing to work.

@maxathousand: I don't think anyone here was harsh. Straight forward and no sugar coating, yes.

The same question can be asked about pressure regulators for water pipes. We just simply don't want things to explode.

This question is more or less identical to the question I asked before I went to university. Now, several years afterwards, I can say that I still don't know why resistors are used. Nah, that was a bad joke.

Well, V = R * I for instance is one basic law of physics you should do some research on.

Thanks to all that commented. I think my biggest issue was that my understanding was that a power source (forced everything it has) into a circuit, and that your job is to "manage: all of that and make it usable. I understand now that you take what you need, and THAT alone changes my understanding on so many other things and concepts. (Thanks high school physics 20 years ago...) I had a great teacher, maybe I just wasn't paying enough attention. ;-)

Possible duplicate of Correct formula for LED current-limiting resistor?

@DmitryGrigoryev, definitely not ;-) I was using the LED as an example to state my gross misunderstanding on the subject of circuits.

Related on Physics.SE (though not nearly as detailed).

@Cort: "I find a lot of people get viscous when the Dunning-Kreuger Effet shows up" I would correct this, but perhaps "viscous" == thicker is very appropriate!

@Louis: I think my best explanation is that a tap (a stopcock) is like a variable resistor. You know why you choose a setting on your bath taps? That's why you choose resistor values. Doing without resistors would be like having your taps always fully open. But then components always have internal resistance. Without even that, a circuit with any energy at all would discharge instantaneously at infinite current and destroy a sizeable part of the universe.

@maxathousand SE can be called "spartan", justifiably. I would'd call SE "savage".