There is a little difference in its and it’s. ‘Its’ means the thing that belongs to him/her/it. While ‘it’s’ is a short form for ‘it is’ like the short form for it will is it’ll. Keep in mind that there are two kinds of usage of any language; formal and informal. In formal writings, can’t, don’t, it’ll, he’ll, he’d and such words are not used. Instead, cannot, do not, it will, he will etc. are used. But it’s is among those words that can be used in formal writings.
So, whenever you see apostrophe (‘), it only have two meanings. If apostrophe is used with word other than s like he’ll, he’d, then apostrophe only means that the word has trimmed to short. If it is used with s, then it has two meanings; one is the same as of the previous one but other means belongings e.g. Ali’s copy, Aslam’s computer, My friend’s book.
Now, let me clear one more thing. From the above explanation, a confusion arose. apostrophe s is used for belongings but I said that if apostrophe s is NOT used with it, then it means belonging and if it IS used it simply means ‘it is’. Definately, this problem would have arose in the minds of the people of the language and hence they made this exception. In all other cases the confusion can’t arise. For example he’s could never be meant that something belongs to him because for that we’ve a genuine word ‘his’. So, he’s only means ‘he is’. So ALWAYS keep in mind that the word it’s is an EXCEPTION.