My concept in Amps in not clear.. Someone please explain it to me..

I know that a Battery rated at
5Ah = 5 Ampere hour
So if 1 Amp is drawn from the battery constantly with a load it will run for 1 Hour..

If a battery is rated at 20C discharge rate, ie. the a load of ( 20 x 5 )Amp can be connected to it. ie. max. 100amp load can e connected to the battery..

Now please explain me how do I control the amp of the battery.. Like the Power Supply unit's current can be controlled..

5Ah = 5 Ampere hour
So if 1 Amp is drawn from the battery constantly with a load it will run for 1 Hour.

Nominally, five hours at one amp, or one hour at five amps, but it rarely works like that.
For instance, a D cell might be rated at 14Ah, but its own internal resistance will limit the actual discharge rate, and the rating is only achievable at very low currents measured in milliamps, so it will last a very long time.

Think of battery like a bucket of water, if you tip the bucket upside down, all of that water flows out instantly (that’s a dead short in the electronics world, except a lot more dangerous than a spilt bucket of water) …

But if you gently tip it out, you control how much you “let out” so 5amps call that 5liters of water, if you can pour out 1liter in an hour that’s 5 liters in 5… but as stated batteries have a weird discharge curve.

So, controlling how much you let out is your current flow 1000mah battery could supply you 500ma for 2 hours or 2000ma for 30 minutes or if the internal resistance of the battery allowed it (Capacitor realms) 10000amps for a brief moment…

The current "drawn" out of a battery is determined by the load you apply to it. Take your 5AH battery and let us say it has a voltage rating of 12 volts.

For the purpose of simple illustration (and calculation) let us neglect the effect of the battery's internal resistance and assume the load is a simple resistor.

With a load resistor of 100 ohms applied across the battery terminals, the current drawn will be 12/100 = 0.12 amps So the battery might be expected to supply this load for 5/0.12 = 42 hours

With a load resistor of 10 ohms the load current will be 12/10 = 1.2 amps and the duration will now be 5/1.2 = 4.2hours

You mentioned 20C and are correct in assuming this means 20 times the battery capacity or 20 x 5 =100A. But very few types of chemistry can sustain to supply this level of current without causing damage. 20C would suggest a total discharge period of less than 3 minutes !

However battery manufacturers frequently rate their batteries at the 20hour rating, which is quite different from 20C. The 20hour rating is based on the battery capacity lasting for 20hours. So in this case the battery would be specified as 5AH @ 20hour rating
For your 5AH battery, and in simple terms, this means it can supply 5/20 = 0.25amps for 20 hours. They generally also specify values for 10hour and 5hour rating

Similarly you will often see manufacturers recommending charge currents based on a C value and an example would be "charge current not to exceed C/7" In your case, using a C/7 figure, the charge current should be limited to 5/7 = 0.7amps

jackrae:
You mentioned 20C and are correct in assuming this means 20 times the battery capacity or 20 x 5 =100A. But very few types of chemistry can sustain to supply this level of current without causing damage. 20C would suggest a total discharge period of less than 3 minutes !

ye, but most LiPo batteries used by RC modelists are able to sustain 10C-20C discharge rate without any damage.
some of them even a lot more : http://thunderpowerrc.com/G8ProForce70C.htm

70C continuous ! for a 1800mAh that makes 126A continuous....never used one of these (30C my maxi), but it certainly gets a little hot when delivering 126A for more than 1mn

If you apply a LED across a 12Volt battery, it will try to dray a large amount of current (amps), and probably burn out from overheating.
If you want to limit the current, you put a resistor in series with the LED, that will limit how much current will flow.

Joy:
How do I control the amp through a circuit..??
I mean the way amp is controlled in Power Supply unit..

You can't control amps in a power supply. Some power supplies have a current limit, a control or feature that reduces the voltage if a set current is exceeded. You can not do this with batteries without a power regulator circuit.

I even believe that the Amp drawn is always determined by the load..

I cannot make out how is current output measured..
I mean to say that amp drawn by a load can be measure by connection a ampere meter in series with the load..

By when I am controlling the charging current in my LiPo charger how is the current output measured..??

OR

How is the output current measured in a Bench Power Supply Unit..

The key to designing a good piece of electronics these days is "Efficiency"

Linear Regulators, Shunt Resistors, Shunt Zeners, Pass Transistor (extra voltage to ground rail)

Basically, they all waste a lot of power in general, the extra power simply turns to heat, so the "less" components turning to heat the more efficient your circuit is, so for example a simple
transistor circuit, you start off with a low current, if you need extra current you switch on a transistor and limit that current... find a power supply which is closely rated to your target
supply voltage, eg if you're feeding a 20v supply but your components only need 5v...

Either change the power supply or buying a switching regulator.