Given the great similarity in spelling and no distinction in pronunciation, it’s little wonder. It’s also sad, really, since knowing how to distinguish between them is very easy.
Its is a possessive personal pronoun. It’s is a contraction for it is.
And because it’s a contraction, there is a very easy way to know when to use it. Just replace the contraction with the expanded form. If it works, the contraction is appropriate. If not, you should use the word without the apostrophe.
Take the example in the cropped image for instance. If you replace the word underlined in red with the expansion for the contraction, does the sentence make sense?
When you remember this simple device, it’s easy to know when to use its and when to use it’s.