El camión llegó temprano.

El means the, while un means a/an.

So el camión llegó temprano means the truck arrived early, referring to a specific truck.
If you said un camión llegó temprano, it would mean a truck arrived early, with no specific truck identified.

The accent mark shows where the stress goes: ca-mión.

Without the accent, Spanish stress rules would make you expect stress on the first syllable, but the correct pronunciation stresses the last syllable: ca-MIÓN.

It is also important for spelling correctness. The word is always written camión.

The accent mark shows both pronunciation and meaning.

• llegó = he/she/it arrived or you arrived (formal usted) in the preterite
• llego = I arrive in the present tense

So the accent is not optional. It changes the form of the verb.

Llegó is the preterite form of llegar.

Here it means a completed past action: arrived.

So:

• llega = arrives / is arriving
• llegó = arrived
• llegaba = used to arrive / was arriving

In this sentence, the truck arrived at a specific time in the past, so the preterite is the natural choice.

In Spain Spanish, both can be possible depending on context, but they are used differently.

• llegó temprano = simple past, a completed event
• ha llegado temprano = has arrived early, often connected more directly to the present

In a simple standalone sentence telling what happened, llegó temprano is very common and natural.

Here temprano means early.

Although tempranamente exists, Spanish usually prefers temprano in everyday speech.

So:

• llegó temprano = arrived early

This is much more natural than llegó tempranamente, which sounds more formal or less common in ordinary conversation.

Here it works as an adverb, because it describes how/when the truck arrived.

It is one of those Spanish words that can be used as:

• an adjective: una hora temprana = an early hour
• an adverb: llegó temprano = it arrived early

So in this sentence, it is modifying the verb llegó.

In most of Spain, ll is usually pronounced like y in modern speech, so llegó sounds roughly like ye-GÓ.

A rough pronunciation of the whole sentence is:

el ca-MYON ye-GO tempr-AH-no

More approximately in IPA for standard Peninsular Spanish: [el kaˈmjon ʝeˈɣo temˈpɾano]

Depending on region, the exact sound of ll can vary a bit.

Yes, if the subject is already clear from context.

Spanish often omits subjects, but here el camión is a noun phrase, not a subject pronoun. You can drop it only when the listener already knows what you mean.

• El camión llegó temprano. = The truck arrived early.
• Llegó temprano. = It/He/She/You arrived early, depending on context.

Without context, llegó temprano is less specific.

This is the most neutral and common word order in Spanish:

subject + verb + adverb

• El camión = subject
• llegó = verb
• temprano = adverb

Spanish is more flexible than English, so you may also hear things like:

• Llegó temprano el camión.

That can sound more marked or context-driven, but the basic version is El camión llegó temprano.

Yes. In Spain, camión is the standard word for truck.

A British English speaker might think of lorry; in Spain Spanish, camión is the usual equivalent.

Depending on context, it can refer to different kinds of trucks, from delivery trucks to larger transport vehicles.

Yes, camión is a masculine noun, so it takes masculine articles and adjectives:

• el camión
• un camión
• camión grande

Grammatical gender in Spanish does not necessarily match real-world sex; objects simply belong to a grammatical gender class. Here, camión is masculine.

Not in this sentence.

Llegar often appears:

• by itself, when the destination is not mentioned: El camión llegó temprano.
• with a when the destination is named: El camión llegó a Madrid temprano.

So this sentence is complete without a preposition because it only tells us when the truck arrived, not where.