La guía nos ayudó a situar el pueblo en el mapa antes de empezar la excursión.

Here la guía most naturally means the guide as a person, probably a female guide.

A few useful points:

• guía can mean both guide (person) and guidebook.
• The article helps:
  • la guía = the guide / the guidebook
  • el guía = usually a male guide
• In this sentence, because ayudó means helped us, it sounds like a person, not a book.

So here La guía is best understood as the guide.

After ayudar, Spanish often uses a + infinitive to say help someone do something.

So:

• ayudar a + infinitive = to help to do / help do
• nos ayudó a situar = she helped us place/locate

This is very common:

• Me ayudó a estudiar = He/She helped me study
• Te ayudamos a encontrarlo = We helped you find it

In English, to is often optional after help, but in Spanish the a is the normal structure here.

Nos means us.

In La guía nos ayudó, it is the indirect object pronoun, showing who received the help:

• La guía = the guide
• nos ayudó = helped us

Compare:

• me ayudó = helped me
• te ayudó = helped you
• nos ayudó = helped us
• les ayudó = helped them / you all

Spanish uses these short object pronouns a lot, and they usually come before the conjugated verb.

In Spanish, object pronouns like me, te, nos, lo, la, le usually go before a normal conjugated verb.

So:

• La guía nos ayudó = correct
• not La guía ayudó nos

You attach pronouns after the verb mainly with:

• infinitives: ayudarnos
• gerunds: ayudándonos
• affirmative commands: ayúdanos

But with a standard past tense verb like ayudó, the pronoun goes before it.

Yes, here situar means something like:

• to place
• to locate
• to situate

In situar el pueblo en el mapa, the idea is to identify where the town/village is on the map.

A native English speaker may find situate a bit formal in English, but in Spanish situar is perfectly normal in this context.

Similar verbs are:

• localizar = to locate
• ubicar = to locate/place
• encontrar = to find

But situar ... en el mapa is a very natural expression for showing where a place is geographically.

Because el pueblo is the direct object of situar, and it is a thing/place, not a person.

Spanish sometimes uses the personal a before a direct object, but mainly with specific people (and sometimes pets or personified things).

So:

• situar el pueblo en el mapa = locate the town on the map
• vi a María = I saw María

You do not use the personal a with ordinary places like el pueblo.

It can mean different things depending on context.

Common meanings of pueblo:

• village
• small town
• people / the people

In this sentence, because of en el mapa, it clearly means a place, so village or town works.

So:

• situar el pueblo en el mapa = locate the village/town on the map

It does not mean people here.

En el mapa is the normal way to say on the map when talking about location.

Spanish often uses en where English uses in or on, depending on context.

So:

• en el mapa = on the map
• en la foto = in the photo
• en la lista = on the list

Sobre el mapa would sound more like physically on top of the map, not shown/located on the map.

After antes de, Spanish uses an infinitive when the subject is the same or when the subject does not need to be stated explicitly.

So:

• antes de empezar la excursión = before starting the excursion / before we started the excursion

This is a very common pattern:

• antes de salir = before leaving
• antes de comer = before eating

If Spanish uses a fully conjugated verb after antes, it normally becomes antes de que + subjunctive:

• antes de que empezara la excursión
• antes de que empezáramos la excursión

That version is possible, but more explicit and less economical. Here antes de empezar is the simplest natural choice.

Because empezar here is being used as a normal transitive verb: to start the excursion.

So:

• empezar la excursión = to start the excursion

The reflexive form empezarse can exist in some contexts, but it is not the neutral, standard choice here.

For a learner, the safest pattern is:

• empezar algo = to start something
• comenzar algo = to begin something

Examples:

• Empezamos la clase = We started the class
• Comenzaron el viaje = They began the trip

Ayudó is the preterite of ayudar because it presents the action as a completed event in the past.

• La guía nos ayudó... = The guide helped us...

This sounds like one finished action that happened before the excursion started.

If you used the imperfect ayudaba, it would suggest:

• a repeated action
• an ongoing background action
• a description rather than a completed event

For example:

• La guía nos ayudaba siempre que íbamos de excursión = The guide used to help us whenever we went on excursions.

But in your sentence, it is one specific completed act, so ayudó fits best.

Yes, both are possible, but the nuance can vary a bit.

• situar el pueblo en el mapa = very natural; to place/locate it on the map
• localizar el pueblo en el mapa = also natural; emphasizes finding it
• ubicar el pueblo en el mapa = understandable and common in many places

A useful regional note:

• In Spain, situar and localizar often sound especially natural in this context.
• ubicar is also correct, though some speakers may feel it is slightly less traditional in certain contexts.

So the original sentence sounds very good for Spanish from Spain.

Yes, somewhat, but the original order is very natural.

Original:

• La guía nos ayudó a situar el pueblo en el mapa antes de empezar la excursión.

Why it works well:

• La guía introduces the subject
• nos ayudó gives the main action
• a situar el pueblo en el mapa explains what she helped us do
• antes de empezar la excursión gives the time frame

You could move some parts for emphasis, for example:

• Antes de empezar la excursión, la guía nos ayudó a situar el pueblo en el mapa.

That is also completely natural.

But the original version is clear, neutral, and well-ordered.

Excursión often means a short trip or outing, especially for leisure, school, tourism, or the countryside.

Depending on context, it might be translated as:

• excursion
• outing
• trip
• sometimes hike

In this sentence, because they are looking at a map before starting, it could be:

• a guided outing
• a countryside trip
• possibly a hike

So excursión is a broad word, and the best English translation depends on the wider context.