"it" is similar to Spanish "lo" in these situations: - I want it (lo quiero) - I know it (lo sé) - give it to him (dáselo) - No, it isn't. (No, no lo es.)

It's used in the 3rd person singular for things, both in subject and object cases, and is the neuter counterpart of the masculine and feminine pronouns "he", "she", "him" and "her", which are used for people. (There is a bit of a grey area for babies of indeterminate sex and for animals, especially pets, which could use "it", but which people often prefer a masculine or feminine pronoun for, seeing that as being more personal.)