I'm still new to electronics and dont fully understand even the basics. I get what most of your basic components do, resistors, caps, transistors etc. But Voltage and Current kinda throws me for some reason. I get the whole water through a pipe analogy but for some reason it doesn't feel like it's clicked with me yet.

I think my biggest question is where does the current come from? Or how do you find it?

If I have a 9v battery, the battery is supplying the voltage of 9 volts, but what current is that? Is that battery specific? I could use Ohm's law to find the current (I = V/R), if I knew the resistance... But I don't, and dividing by zero, well, that's no good.

My understanding, and back to the analogy of the water pipes, is voltage is the pump and current is the direction and speed of the electricity. Does that mean the more voltage the faster the current (assuming no resistance)?

First off, I'm a little confused which way the current actually flows. Does it go from negative to positive or positive to negative? I've heard it goes from - to + but then why are diodes "backwards" - the current flows the direction of the arrow. Really confusing.... x_X

Anyways, back to voltage and current.

Let's say I plug the voltage and ground rails of a breadboard into an arduino's 5 volt and ground pins. Then I add one LED to the breadboard and power it up. *Let's ignore resistors for right now to try and hopfully keep things simple.

Let's say the LED is this:

https://www.sparkfun.com/products/5313.4V forward drop

Max current 20mA

What do those specs mean? 3.4V forward drop. Does that mean if I apply 5V to the anode it will drop to 1.6V out the cathode? So if that were true then if I put a second LED in series it should be less than half as bright, no?

Max current makes sense... That's the max amount of current you can give it before it fries. But again, I don't know how you figure current.

If I wanted to light 10 LED's how would I figure out what I need?

Also, I've seen people but resistors on the anode side (which makes sense to me, if that's the way current flows) and then I've seen them put them on the cathode side - whats going on here?

Maybe I dont really understand the relationship between voltage, current and resistance.

I'll leave it at this for now. And give you guys a chance to respond if you think you can help me. I know I have a lot (and a little scattered) of questions but I dont really know exactly where to start asking.