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Have you ever thought about how and why devices turn ON only at some specific voltages. and below which it keeps shutting off. 
Like, this red led only turns ON above 1.4v but below this it remains OFF. Similarly with this motor, it won’t turn ON below 0.5V but starts rotating above it. On the other hand, microcontroller have clear specification, that this will turns ON at 5V (operational voltage). And it is not just with this one only, each and every device like, TV, Fan, Refrigerator all of them have their own turn ON voltage and below this they won’t work at all.

Well, I can explain all this, with just one example.
Here, I have a welding machine and its ON. As soon as I touched its positive and negative terminal with any metals. It sparks because large current running through it.
But if my skin comes in contact of it, nothing actually happens. I mean once I touched these electrodes to the metal it starts giving sparks because large amount of current was passing through this. On the other hand, same thing is not happening with me.
All because the voltage in this machine is around 90V which is not enough to make charges flow from my body, but if this voltage gets big enough, I can easily get cooked. But why why and why?

Thats all happening because of both voltage and resistance values.
Listen carefully 

Voltage actually pushes charges from one location to the other, while resistance does exactly opposite of it. Means resistance do not let charges to move easily, it resist the flow of charges.
If in any ways charges moves or flow we can say that current is flowing.
And this can only happens when voltage pushing force is larger than resistance resisting nature, charge will move and current will get created.
But, if voltage is weaker in front of resistance resisting nature, charge won’t move, or we can say that current will not get created.

So, here in this experiment resistance of my body is large enough what won’t let voltage to make charge flow from my body. But this won’t keep working forever if this voltage value gets large enough roughly around 100v this will counter my body resisting properties, and charges will starts flowing into me and I will get shocked easily.

Similarly, Lower than operational voltage of LED, or motor won’t turning these ON. because this much of voltage cannot win again the resistance of it. And to make voltage win, we have to increase the amount of it. So that charge and move again the resistance and creates current.
And now you can easily understand by reading the label of this TV, or refrigerator. 
And also, now I have a question for you, can you tell me why? TV or refrigerator before decades were requires a lot of voltage. and it requires now.

And also in fast charging smartphone, there internal resistance is quite low, so that when we apply some voltage into it, more charges can get transferred into the battery and that charges it quickly.

and if resistance of battery is quite high, less charge will get transferred into it for the same voltage. means not so fast charging.

So, now let’s summaries everything using physics formula of class 10.
here, voltage means a pushing force that pushes negative charged atom from one place to another that is called work. In actual its called emf ( means electromotive force ) but lets skip it for now, and consider it like voltage and its completely fine.

so, voltage = work / charge.

and current I = charge /time. Don’t you think its look like speed formula, as speed = distance /time.
therefore, we can say that speed of charges means current.  more speed of charge larger will be current.

As you can see, how fast charges will flow. It depends on voltage, because this is the one that pushes it to move.
But, one more thing, current speed also depends upon the resistance. because its resist the flow of it ‘Just Like friction but not exactly’. 
and as per the perspective of the resistance of wires, 
Formula of resistance is, R = pl/A

means resistance depends upon,
the material from which wire is made of (p) and as
‘R’ is directly proportional to ‘l’ long wire have high resistance and short one has less resistance and
‘A’ is inversely proportional to ‘R’, larger the area of wire, lesser will be wire’s resistance and lesser its area, more will be wire’s resistance.

And one more formula, that gives a proper relationship between voltage current, and resistance is as you know already,
V = I R,
and on this, we will talk about later.

and you can check out written blog of this video, from my website. if you want. and make sure to check out the bottom of video description for more recommended video, to enhance your engineering concept.
Thanks for watching, make yourself like your existence creates some value to living beings.
bye bye.