There are about a dozen Spanish verbs which must be conjugated with an indirect object pronoun, such as gustar and importar. This grammatical construction does not exist in English, but it’s not difficult once you get used to it.
An indirect object is a person that someone or something does something to indirectly. In both Spanish and English, indirect objects are often replaced with indirect object pronouns.
Lo is the Spanish neuter direct object pronoun, used to mean "it" when referring to something non-specific or with no gender, such as an idea, adjective, situation, or clause.
Spanish negative pronouns (nada, nadie, ninguno) replace and simultaneously negate nouns. They may be the subject or object of the verb they’re used with.
Object and reflexive usually precede the verbs they modify. However, in the case of infinitives, gerunds, and affirmative commands, they often get attached to the end of the verb instead.
Spanish prepositional pronouns are used after prepositions, logically enough, often in order to emphasize the noun they replace, and are thus a sort of subcategory of the disjunctive or stressed pronouns found in other languages.
The relative pronoun quien joins a main clause to a dependent or relative clause, replaces one or more words, and can only refer to people. The plural form is quienes.