Hi mate,
First of all the best way to learn is by trying, and also talking to the vendors in vaping shops too!
A clearomizer is a type of tank - a tank just means a reservoir that holds the liquid; a clearomizer is as far as i understand, a 'transparent' tank system so you can see the liquid inside.
Heating wire resistance is much more important and is a measure of how much heat or energy your heating wire produces for a given voltage. Low resistances produce more heat and vapour then high resistance wires... this depends on what voltage you are using... so for an ego device running at 3.7 volts, a 3 ohm atomiser wont produce as much vapour as a 1.5 ohm. But its up to you how much throat hit you want, and also depends on the liquid type since some can burn at hotter temperatures which produce burnt tastes.
Learn by trying! I bought all kinds of atomisers when i first started and slowly found the ones i preferred. good luck