The confusion between "it's" and "its" is common, but there's no secret behind these forms.
It's is the short form for it is or it has.
Resolva exercícios e atividades acadêmicas
Its is a pronoun, like her or his.
Examples:
Encontre o professor particular perfeito
The pen is blue. It is blue. or It's blue.
The plane has already arrived. It has already arrived. or It's already arrived.
One of the chair's parts is missing. - One of its parts is missing.
Understood? :))
