La ruĝa semaforo igis nin halti, kaj granda kamiono atendis maldekstre de nia veturilo.

La is the definite article, meaning the.

So:

• la semaforo = the traffic light
• ruĝa = red

The ending -a shows that ruĝa is an adjective. In Esperanto, adjectives usually come before the noun and must match it in number and case when needed.

Here:

• ruĝa modifies semaforo
• both are singular
• neither has an accusative -n

So la ruĝa semaforo simply means the red traffic light.

Yes. Semaforo means traffic light or traffic signal.

It is a noun, so it ends in -o:

• semaforo = traffic light
• la semaforo = the traffic light

For English speakers, it is useful to notice that Esperanto often uses internationally recognizable roots, and semaforo is one of them.

Igis comes from the very important Esperanto suffix -ig-, which gives a causative meaning: to make something happen or to cause someone/something to do something.

Here is the breakdown:

• igi = to make, to cause
• igis = made, caused

So:

• La ruĝa semaforo igis nin halti = The red traffic light made us stop

A very common pattern is:

• igi + object + infinitive

So in this sentence:

• igis = made
• nin = us
• halti = stop

Literally: made us stop.

Because nin is the direct object form of ni.

• ni = we
• nin = us

In the sentence, the traffic light made us do something, so us is the object of igis.

Esperanto marks the direct object with -n, so:

• mi → min
• ni → nin
• li → lin

That is why nin is correct here.

Because after igi, Esperanto normally uses the infinitive.

The structure is:

• igi iun fari ion = to make someone do something

So:

• igis nin halti = made us stop

Here:

• halti = to stop
• it stays in the infinitive because it depends on igis

Why not haltis?

• haltis means stopped
• but that would make it a separate finite verb
• after igis, Esperanto wants the infinitive: halti

Why not haltiĝi?

• halti already means to stop
• you do not need -iĝ- here

So igis nin halti is the normal and natural way to say made us stop.

Halti usually means to stop in the intransitive sense: to come to a stop.

Examples:

• La aŭto haltis. = The car stopped.
• Ni haltis ĉe la lumo. = We stopped at the light.

If you want to say stop something in a causative sense, Esperanto often uses another construction, such as haltigi:

• Li haltigis la aŭton. = He stopped the car.

In your sentence, igis nin halti means the red light caused us to come to a stop.

Because granda kamiono is being presented as a large truck, not the large truck.

Compare:

• granda kamiono = a large truck
• la granda kamiono = the large truck

Esperanto does not have a separate word for a/an. Indefiniteness is usually shown simply by leaving out la.

So:

• granda kamiono atendis... = a large truck was waiting...

Granda means large or big.

It comes before the noun because that is the usual order in Esperanto:

• granda kamiono = large truck

The ending -a shows it is an adjective.

Like other adjectives, it agrees with the noun if necessary. Here both words are singular and not accusative, so there is no extra ending:

• granda kamiono

If it were plural, you would get:

• grandaj kamionoj = large trucks

It can mean either, depending on context.

Esperanto has a simple past tense in -is, and it often covers both:

• waited
• was waiting

So:

• granda kamiono atendis...

can naturally be understood as:

• a large truck waited...
• a large truck was waiting...

In this sentence, English would usually prefer was waiting, but Esperanto does not need a special past continuous form here.

Maldekstre de means to the left of.

It is built like this:

• dekstre = on the right, rightward
• mal- = the opposite
• maldekstre = on the left, leftward
• de = of / from

So literally, maldekstre de nia veturilo is on the left side of our vehicle.

This is a very common Esperanto pattern:

• dekstre de = to the right of
• maldekstre de = to the left of

The prefix mal- is extremely common in Esperanto for making opposites.

Because maldekstre de is the fixed way to express position relative to something.

So:

• maldekstre de nia veturilo = to the left of our vehicle

Here de does not mean movement away from something. It is just part of the expression showing relative location.

Also, after a preposition like de, Esperanto normally does not add the accusative -n. That is why you get:

• de nia veturilo
• not de nian veturilon

Veturilo means vehicle.

It is more general than aŭto:

• aŭto = car
• veturilo = vehicle

So nia veturilo can mean:

• our car
• our truck
• our vehicle

depending on context. If the translation you were shown says our vehicle, then veturilo is a good match because it stays general.

The comma separates two main clauses:

• La ruĝa semaforo igis nin halti
• kaj granda kamiono atendis maldekstre de nia veturilo

Esperanto punctuation is fairly flexible, but using a comma before kaj when joining two full clauses is very common and helps readability.

So the comma is not mysterious grammar; it is just normal punctuation.