Le soir, ils écoutent le guide raconter des légendes locales sur le volcan.

French usually uses le + part of the day to talk about a general time (in the evening, in the morning, etc.):

• le matin – in the morning
• l’après-midi – in the afternoon
• le soir – in the evening
• la nuit – at night

So Le soir here means In the evenings / At night (generally, habitually).

Dans le soir and au soir are not natural in standard French for this meaning.
If you want to talk about a specific evening, you would say:

• Ce soir – this evening
• Un soir – one evening / some evening

Yes. You can also say:

• Ils écoutent le guide raconter des légendes locales sur le volcan le soir.

Both are correct.
Putting Le soir at the beginning emphasizes the time a bit more (setting the scene: As for the evenings…), while putting it at the end is a bit more neutral. It’s mostly a matter of style and focus, not grammar.

With verbs of perception (see, watch, hear, listen to, feel, etc.), French often uses this pattern:

[perception verb] + [direct object] + [infinitive]

Examples:

• Ils regardent les enfants jouer. – They watch the children play.
• J’entends le vent souffler. – I hear the wind blowing.
• Ils écoutent le guide raconter. – They listen to the guide tell…

You do not add à or de between le guide and raconter in this structure.
If you insert à or de, it changes the grammar and often becomes wrong or unnatural here.

Both can be correct, but there is a nuance.

• Ils écoutent le guide raconter des légendes.
  Focuses on the action they are listening to (the guide in the act of telling stories). This is the standard “perception verb + infinitive” structure.

• Ils écoutent le guide qui raconte des légendes.
  Grammatically fine, but it feels more like: They listen to the guide, who tells legends… The relative clause qui raconte adds information about le guide, instead of forming one tight verbal unit écouter + le guide + raconter.

In practice, for “They listen to the guide telling local legends…”, the version with the infinitive (écouter le guide raconter) is more idiomatic.

Le guide uses the definite article (le) and therefore refers to a specific guide that the speaker and listener know about (for example, the guide leading their tour that evening).

• le guide – the guide (the known/identified guide)
• un guide – a guide (any guide, not yet identified)
• leur guide – their guide

In a typical story or description, once a guide has been introduced, French naturally uses le guide to refer back to that known person.

Here des is the plural indefinite article, meaning some (but usually left untranslated in English):

• une légende locale – a local legend
• des légendes locales – (some) local legends

So des is not the preposition de + les in this sentence; it’s just the plural form of un/une:

• un → des
• une → des

Most French adjectives go after the noun, and local is one of those:

• une légende locale
• des légendes locales

Only certain common, short adjectives (often summarized as BAGS: Beauty, Age, Goodness, Size) usually go before the noun, like:

• une belle histoire
• un vieux château
• un bon guide
• un petit village

Since local(e) is not in that group, it naturally comes after the noun.

Adjectives in French agree in gender and number with the noun they describe.

• légende is feminine singular → une légende locale
• légendes is feminine plural → des légendes locales

So:

• Feminine: locale
• Feminine plural: locales

Other forms:

• Masculine singular: local
• Masculine plural: locaux
  (e.g. des volcans locaux – local volcanoes)

The basic literal meaning of sur is on (physically on top of something), but with some nouns, including topics, sur can also mean about / concerning:

• un livre sur les volcans – a book about volcanoes
• un film sur la guerre – a film about the war
• des légendes sur le volcan – legends about the volcano

In this sentence, it clearly means about the volcano, not physically on it.

French uses the simple present for:

• actions happening right now
• habitual or repeated actions

The time expression Le soir here shows that it’s habitual:

• Le soir, ils écoutent le guide…
  → In the evenings, they (usually) listen to the guide…

So the French present often corresponds to English present simple (“they listen”) or even present progressive (“they are listening”), depending on context.

You replace le guide with the direct object pronoun le (him) and keep the same structure:

• Ils l’écoutent raconter des légendes locales sur le volcan.

Notes:

• l’ is le before a vowel sound (écoutent).
• The pronoun goes before the conjugated verb (écoutent), not before raconter.

Key points:

• ils écoutent → liaison between ils and écoutent:
  • sounds like: [il zé-koot]
  • final -ent in écoutent is silent.
• le guide:
  • guide sounds like [gid] (final e is very weak / almost silent).
• raconter:
  • ra-con-ter → [ra-kɔ̃-te], with nasal [ɔ̃] in -con-.

So, fairly closely:

• Le soir, ils écoutent le guide raconter…
  → [lə swaʁ il zé-kut lə gid ra-kɔ̃-te] (approximate phonetics for learners).