"This is an interesting book."
Translation:Este es un libro interesante.
When do I use "este" and when do I use "esto?" Arent they both the male forms of "this"?
Este (masculine form for THIS) is used here becuase we know the pronoun is refering to el libro, a masculine object. Compare to Esto es interesesante. When we don't know the reference point, we use the neuter form. Hope that helps. The esto, este, esta etc. thing can be confusing.
I believe "esto" is gender-neutral and should only be used when the gender is unknown while "este" should be used for male antecedents.
I was just in Ecuador and I asked this question of Ecuadoreans and an Argentinian. Both were a bit stumped themselves (we don't give much thought to grammar in our native tongue after primary school!), but agreed that esto is generally at the end of a sentence. Like, "¿De quién es esto?" "Este libro es mío."