El chico dice: «Adelante».

El is the masculine singular definite article, meaning the.

So:

• el chico = the boy
• chico by itself can mean boy in a more general sense, depending on context

In this sentence, el chico refers to a specific boy, so Spanish uses the article.

Chico usually means boy or young man, but it can also mean small as an adjective in other contexts.

Here it is a noun:

• el chico = the boy

Related forms:

• la chica = the girl
• los chicos = the boys or sometimes the kids
• las chicas = the girls

In Spain, chico/chica is very common in everyday speech.

Dice is the third person singular present tense of decir.

So:

• yo digo = I say
• tú dices = you say
• él / ella dice = he / she says

Since the subject is el chico (the boy), you need dice.

Other forms you mentioned are different tenses or persons:

• dijo = he/she said
• di = I gave / I said?
  Actually di is from dar (I gave) or the tú command of decir (say!) depending on context, so it does not fit here.

Yes, Spanish could say Dice: «Adelante» if the subject is already clear from context.

Spanish often leaves out subjects because the verb ending already gives information about the person and number.

But in this sentence, el chico is included because:

• it identifies who is speaking
• it may be introducing a scene or narration
• it sounds clearer if the subject has not been mentioned yet

So both are possible, but El chico dice: «Adelante» is more explicit.

Here adelante is an expression used on its own, not a full sentence with a verb stated explicitly.

Depending on context, adelante can mean things like:

• Come in
• Go ahead
• Carry on
• After you

It literally relates to the idea of forward or ahead, but in real use it often works as a set phrase.

For example:

• Someone knocks at the door → Adelante = Come in
• Someone hesitates before speaking → Adelante = Go ahead

Functionally, yes, it often works like a command or invitation, but grammatically it is not a regular imperative verb form like pasa or entre.

It is more like a fixed adverbial expression that speakers use to encourage movement or action.

That is why it can sound natural in several situations:

• Adelante. = Come in.
• Adelante. = Go ahead.

So it behaves like a command in meaning, even though its grammar is a bit different.

The colon introduces the exact words the boy says.

So:

• El chico dice: ... = The boy says: ...

This is similar to English writing like:

• The boy says: Come in.

Spanish commonly uses a colon before direct speech, especially in narrative or formal writing.

Those are called angle quotes or guillemets.

In Spain, they are a traditional and very common way to mark direct speech in writing:

• «Adelante»

You may also see “Adelante” in some texts, especially depending on style, publisher, or digital formatting, but « » is very standard in Spain.

So this is mainly a punctuation convention, not a change in meaning.

In Spain, dice is pronounced approximately DEE-theh in much of the country, because c before e is pronounced like the th in thin.

Very roughly:

• di = like dee
• ce = like theh

So in much of Spain: DEE-theh

In many parts of Latin America, it would sound more like DEE-seh.

Chico is pronounced approximately CHEE-koh.

Breakdown:

• chi = chee
• co = koh

The ch sound is like English ch in cheese.

So:

• chico ≈ CHEE-koh

Not here.

It appears after a colon and inside quotation marks as a single spoken word, so it stays lowercase:

• El chico dice: «Adelante».

You would only capitalize it if normal capitalization rules required it, for example at the beginning of a sentence.

This follows Spanish punctuation style.

In Spanish, the final punctuation often belongs to the main sentence rather than being automatically placed inside the quotation marks. So you get:

• El chico dice: «Adelante».

This differs from standard English, where punctuation often goes inside quotation marks more regularly.

So the placement here is normal for Spanish typography.