Here are some sites offering free courses for beginners. Have look at a few, and discover which one(s) suit your approach.

http://www.allaboutcircuits.com
series of online textbooks covering electricity and electronics

http://www.learnabout-electronics.org/index.php
Descriptions of components and principles, good diagrams, animations, & fault-finding techniques

http://www.satcure-focus.com/hobby/index.htm
Useful range of ideas tutorials circuits links etc

http://electronics-for-beginners.com/links.php

http://www.hobby-hour.com/electronics/
Teaching from basic principles, resistor code calculators, projects

http://www.radio-electronics.com
Useful information and tutorials

http://www.electronics-tutorials.ws/index.html
Plus calculators & tools

An electric fence, with thousands of Volts connected to it, not kill an animal or a human being to touch her, in normal conditions. It turns out that animal or person will lead a uncomfortable shock, but not suffer further damage to discomfort.
What happens is that human skin, in normal state has a resistivity too high and does not allow the current that passes through the body is in itself sufficient to cause damage to person or animal.
But if the human skin is damaged, with a wound or any product that reduces the natural resistance of the skin, then pull on a device electric, even a 1,5VDC battery, the current will pass through the body of the person can be enough to cause damage and even death.
ELECTRIC CIRCUIT everything can be replaced by a battery and a resistor, with battery sinificando the power supply and resistor meaning throughout the circuit outside of it. While the conditions of the external circuit remain normal, the current drawn from the battery, it will be normal and not cause damage to the circuit, but change these conditions and anything can happen, either for more, or to less.
When we study electricity, also learned that a power supply can be represented by a ideal battery, associated with an internal resistor which will limit the amount of current that the battery will provide to power the external circuit, in normal working conditions. Above parameters designed beforehand, this resistor does not interfere in the functioning of the external circuit, but out of those patterns that internal resistor passes to influence and battery stops behaving in the normal way, limiting the voltage and current supplied by the power supply.
When we buy a 8Amps booster, the manufacturer guarantees that, in normal conditions, that will provide booster Zero to 8Amp to our layout, without their characteristics change. Above 8Amp, the manufacturer tells us that a circuit protection (if it exists) will become operational, changing the characteristics in a controlled mode, so he does not burn himself or has damaged its integrity.
The manufacturer does not guarantee that, if in your layout there is any device that collapses with any current value between zero and 8Amps it will not be damaged.
When we connect this booster to our Layout, everything connected to it will work in a normal way, if it is within its normal characteristics and the total ccorrente requested from the Booster is within these limits Zero to 8Amps.
Above this limit, the Booster protection circuit will enter in service, only PROTECTING THE BOOSTER against damage, until the limit set in your project.
If the problem in layout, is not controlled in time or extrapolate Booster protection limits, itself will be damaged.
So in our layout we use a Booster 8Amps to feed a N scale locomotive that consumes 100mA, nothing will happen to the locomotive and it will work normally. However, if your engine be short circuit and request the Booster ten times more current (1Amp), for the Booster it will be as if everything was normal, even if the current is enough to make our little engine catching fire.
Protection circuits may also be present within the locomotive decoder, protecting it from damage, such as a locked motor, but always within predefined limits in circuit design.
There is no universal protection for anything that happens.
Everything works within the parameters established in projects and what extrapolate these limits, will be unprotected.
It is up to us to establish what we do when we designed our Layouts.
Greetings
J.Oscar / RJ from Brazil

Frank. DCC especially Digitrax will run an HO DC engine OK using a ZERO-Zero code, Not sure if the other systems do. I would not let it sit at idle though as it is a higher voltage and constant to the engine motor as it is usually connected to the frame direct. I have a Kato Amtrak Engine that is only DC and on the box it says not to put it on DCC without the chip as you will burn the motor up. (the motors are in the trucks and are probably a little different). But that is OK as I have the new DCC chip now to install so it will not be long for me to run in style anyway.
Digitrax has a setting that you set for HO or N Scale. I am not sure what that limits though, I Will have to look that up. I am not sure if the other systems do that.
I still would not run an engine much on that Zero-Zero code as it can still heat up the motor. It is really just to be able to see how it runs on the system. The engine was made in 1962 and does not have a can motor on it. That run was done on the zero-zero code on Digitrax system and ran fine. But we did not run with a load and only a few times around and on DCC the voltage is a little higher. We also did not leave it in the stopped position as without the chip the motor will get the higher voltage all the time.
from Newman Atkinson

Hi Frank I agree with Sylvain if u need more power because u are expanding use a booster or u can’t afford a booster u can use a computer power pack which is know more then 5 amps.