Me gusta hablar en voz baja en la biblioteca.

In Spanish, gustar does not work like to like in English.

• Me gusta literally means "it is pleasing to me."
• me = to me (an indirect object pronoun)
• gusta = is pleasing

So the structure is closer to "Talking quietly in the library is pleasing to me" than "I like..." in terms of grammar.

Yo gusto would mean "I please" (other people), which is almost never what you want in this kind of sentence.

The subject of gusta is the action hablar en voz baja en la biblioteca (speaking quietly in the library).

• Me = to me (indirect object)
• gusta = is pleasing
• hablar en voz baja en la biblioteca = what is pleasing (the subject)

Any verb in the infinitive (like hablar) or a whole infinitive phrase can act as the subject of gustar and it always uses gusta (singular).

After gustar, when you like doing an activity, Spanish uses the infinitive (the "to do" form):

• Me gusta hablar = I like to talk / talking
• Me gusta leer = I like to read / reading

Using hablo (I talk) would change the structure:

• Me hablo means "I talk to myself" (reflexive), which is not what the sentence says.

So you must keep hablar in the infinitive after me gusta when you’re talking about liking an activity in general.

No. That would be incorrect in this context.

• To express "I like speaking quietly…", Spanish uses the infinitive:
  Me gusta hablar en voz baja…

The gerund (hablando) is used more like "while speaking" / "speaking (at this moment)", not as the object of gustar. For example:

• Estoy hablando en voz baja. = I am speaking quietly.
• Entró hablando en voz baja. = He/She came in speaking quietly.

But with gustar, stick to the infinitive: Me gusta hablar…

En voz baja literally means "in a low voice" and is the natural way to say "quietly / in a low voice" in Spanish.

• voz = voice
• baja = low (feminine, agreeing with voz)

Using bajo alone would mean "under" or could be an adjective for a masculine noun (like un hombre bajo = a short man).
So hablar bajo can be heard in some regions, but hablar en voz baja is clearer and very standard for speaking quietly.

They are different:

• hablar en voz baja = speak quietly / in a low voice (volume)
• hablar despacio = speak slowly (speed)

So:

• In a library you usually want people to speak quietly, not just slowly.
  That’s why en voz baja is used here.

en generally means in / at / on.

Here, en la biblioteca means in the library or at the library (location where the action happens).

a la biblioteca means to the library (movement toward a place), as in:

• Voy a la biblioteca. = I’m going to the library.

Since the sentence talks about where you like to speak quietly (not where you’re going), en la biblioteca is correct.

biblioteca is a feminine noun, so it takes la:

• la biblioteca = the library

In this sentence, you normally keep the article:

• Me gusta hablar en la biblioteca. ✅

Dropping the article (en biblioteca) is not natural here. Spanish uses definite articles more often than English, especially with common places like la biblioteca, el parque, la escuela when referring to them in a general sense.

Yes, Spanish word order is quite flexible. All of these are correct and natural, with slightly different emphasis:

• Me gusta hablar en voz baja en la biblioteca.
  Neutral, basic order.

• En la biblioteca me gusta hablar en voz baja.
  Emphasizes in the library (maybe contrasting with other places).

• Me gusta en la biblioteca hablar en voz baja.
  Possible, but less common and sounds a bit more marked or poetic.

The original is the most neutral and typical for learners to use.

me is an indirect object pronoun meaning "to me".

With gustar, you change this pronoun to say who something is pleasing to:

• Me gusta… = I like… (It is pleasing to me.)
• Te gusta… = You like… (It is pleasing to you, informal singular.)
• Le gusta… = He/She/You (formal) like(s)… (pleasing to him/her/you)
• Nos gusta… = We like…
• Les gusta… = They / You all like…

Example with the same sentence:

• Te gusta hablar en voz baja en la biblioteca.
  You like to speak quietly in the library.
• Les gusta hablar en voz baja en la biblioteca.
  They like to speak quietly in the library.

gusta vs gustan depends on what is liked, not on who likes it.

• Use gusta when the thing liked is singular or an infinitive verb/verb phrase:

  • Me gusta el libro. (one book)
  • Me gusta hablar en voz baja. (the activity of speaking quietly)

• Use gustan when the thing liked is plural:

  • Me gustan los libros. (books)

In Me gusta hablar en voz baja en la biblioteca, the "thing" liked is the activity of speaking quietly, which is expressed by the infinitive hablar, so you use gusta (singular).

You still keep gusta, because the thing you like is still the activity of speaking (an infinitive):

• Me gusta hablar en voz baja en las bibliotecas.

Here:

• Me gusta = I like
• hablar en voz baja = speaking quietly
• en las bibliotecas = in libraries (plural)

Even though bibliotecas is plural, the grammatical subject of gusta is still the infinitive hablar, so the verb stays gusta, not gustan.