In the name of Allah, the Most Gracious, the Most Merciful,
It's a good day for the cat today. It has managed to get out of its cage.
It's is used when the phrase 'it is' is shortened to one word.
Its is used to show possession for the pronoun it. Like 'his' for a he and 'her' for a she, 'its' is for it.
This is grammar and I'm sorry if this entry slowed your learning process.
Allah knows best.