Say the car and its doors: 'its' sits before a noun and cannot stand alone. That placement test identifies it as a possessive determiner, the class that includes my, your, his.
Possessive words and how to tell them apart
Possessive determiner. The clue is position: a possessive determiner always sits directly before a noun. That is her laptop. Its belongs to this same class as my, your, his: it is a possessive determiner because it precedes a noun, as in the garden and its gate.
Possessive pronoun. The clue is that it replaces the noun entirely, standing alone. That laptop is hers. Hers carries the full meaning of her laptop by itself.
Same form, both classes. His genuinely occurs in both: his car shows the determiner, while That car is his shows the pronoun. The noun test separates the two uses of one spelling.
Paired partners. Some forms never cross over: my is only a determiner, and mine is only a pronoun, as in This seat is mine. When a noun follows, use the determiner form; when no noun follows, use the standalone partner: my seat but This seat is mine.
When the test needs one refinement: 'its' vs 'it's'
Some confusion comes only from spelling. It's with an apostrophe is not a determiner at all; it is the contraction of it is or it has, as in It's raining. If the sentence still works when you say it is, write the contraction, and the possessive determiner its is out of the picture.