Nitrogen Cycle / Cycling of tank

This is a famous Newbie question, what is cycling of tank? i got this question uncountable times and its really a big headache for me to explain from start to end as most newbie to planted tank /Shrimp tank does not seem to like googling and researching... well, I will try to simplify in common english/singlish/manglish.

Cycling of tank does not mean phyiscally cycling using a bike in an aquarium...duh... its trying to create a bunch/colony of Beneficial Bacteria(BB) to eat up any possible ammonia,no2 and this process is called nitrogen cycle. 

Nitogen Cycle

Ammonia(NH3) is considered poisonous to fish and livestock even in low amount. However, it is commonly introduced into tank via aquasoil, fertilizer, decomposed stuffs, tap water etc sources. Thus having a colony of Beneficial Bacteria(BB) is very important to quickly eliminate NH3

BB will convert Ammonia(NH3) in the tank, thus reducing/eliminating it and producing Nitrites(NO2). So now, we have lesser ammonia in the tank, but we now have another chemical to deal with - N02. If you have a test kit, you should be able to see the nitrite levels rise around the end of the first or second week.

BB will convert the NO2 into nitrates(NO3). NO3 are not as harmful as NH3 or NO2, but NO3 is still harmful in large amounts. The quickest way to lower NO3 is to perform partial water changes or add water conditioner.

Ammonia, Nitrite and Nitrate although are toxic and poisonous, they are considered as plant fertilizer/nutrient therefore having them means its good for plants. However, having more than required may cause death to livestock or invite algae....

Update: NH3 only exists in high PH area, and it will be converted to ammonium (NH4) which is harmless in low PH area. this information was shared by ada website... great infomation as most of us are keeping livestock in low PH water..thus risk of NH3 poisoning is lower

Simplest explanation I can think off:-
NH3 convert into No2 convert into No3 with help of BB with sufficient oxygen

Recommended levels for planted tank with hardy livestock 

ammonia;- 0-0.5 ppm

nitrite;- 0-10 ppm

nitrate;- 0-40 ppm

The above parameters are from my own observation for keeping hardy fish and shrimps, for advance shrimps, its best to keep all NH3,NO2,NO3 at 0 at all times but its quite hard for planted tank as the fertilizer we dose contains ammonia most of the time. So the choice is yours Nice Shrimps or Nice Planted tank.

So is it essential to cycle the tank?? the answer is:- YES if you are keeping any livestock. 
How long does i need to cycle the tank?? the answer is;- to reach 0 for NH3, its norm for ADA soil user to cycle for 1-2 months

So what is the consequences of not cycling the tank properly? The answer is;- death of livestock such as less hardy fish or shrimps.

Ways of reducing cycling time

• Use of commercial BB in a bottle
• Use of commercial water treatment like seachem prime
• Use Aged tank water/filter media to introduce BB faster rather than building BB colony from scratch
• Use of commercial shrimp soil (less fertile for plants though)

IMPORTANT

Notes:- You need oxygen for the nitrogen cycle to work, Do remember to add anti chlorine into water aged the water prior Water Change. Chlorine is poisonous and will kill any BB or livestock...that is why chlorine are added into tap water.