Its "It's" or "Its"

The use of aphostophy in any word brings the meaning "of", i.e., when I say Gyanee's Cat fundae it means 'CAT fundae of Gyanee'. But the usage is very different when it used with the word 'it' and many people dont realise this. So here comes a simple explanation to the word usage

Its
"Its" means 'of it'. Hence the sentence "I took bought a cat online. Its colour is white" is right.

It's
"It's" does not mean "of it". It is a short form of "it is" or "it has". E.g., "It's a very good novel" , "It's been a long time since I took a mock CAT"