It’s:
This is the contraction of “it is” or “it has” and is never used to mark the possessive.
It’s raining outside. (यहाँ बारिश हो रही है बाहर।)
It’s been a long time since we met. (हमें मिले हुए बहुत समय हो गया है।)
Its:
This is the possessive of “it” and, unlike other possessives, does not use an apostrophe.
The dog wagged its tail. (कुत्ते ने अपनी पूँछ हिलाई।)
The company changed its policy. (कंपनी ने अपनी नीति बदल दी।)