A amizade delas começou na escola, antes do relacionamento.

In Portuguese, it is very common to use the definite article with abstract nouns like amizade when talking about a specific friendship.

So a amizade delas means their friendship or more literally the friendship of theirs.

If you said just amizade, it would sound more general, like friendship as a concept.

• A amizade delas começou... = their friendship began...
• Amizade é importante. = friendship is important.

Delas means of them / their, referring to a group of females.

So:

• a amizade delas = their friendship (their = belonging to those women/girls)

Portuguese often prefers dele/dela/deles/delas instead of seu/sua/seus/suas when there could be ambiguity.

For example, sua amizade could mean:

• your friendship
• his friendship
• her friendship
• their friendship

Because of that, a amizade delas is clearer.

Because elas is a subject pronoun, while delas shows possession.

• elas = they
• delas = of them / theirs

In the sentence, we need a possessive idea: the friendship of them. That is why delas is used.

Compare:

• Elas começaram na escola. = They began at school.
• A amizade delas começou na escola. = Their friendship began at school.

Começou is the preterite of começar.

• começar = to begin
• começou = began

The preterite is used for a completed event in the past. Here it marks the moment when the friendship started.

So A amizade delas começou na escola means that the friendship started at some point in the past, specifically while they were at school.

Na is a contraction:

• em + a = na

So:

• na escola = in/at the school

This kind of contraction is very common in Portuguese:

• no = em + o
• na = em + a
• nos = em + os
• nas = em + as

So começou na escola literally means began in the school, but in natural English it is usually began at school.

Portuguese uses articles more often than English does. Even where English might say simply at school, Portuguese commonly says na escola.

So the structure is natural in Portuguese:

• na escola
• no trabalho
• na faculdade

English often drops the article in places like at school, at work, but Portuguese usually keeps it.

It means before the relationship.

Here:

• antes = before
• do = contraction of de + o
• relacionamento = relationship

So literally it is before of the relationship, but in correct English: before the relationship.

The sentence suggests that first they were friends, and only later did they become romantically involved.

Because antes often connects to a noun phrase with de.

So Portuguese says:

• antes de viajar = before traveling
• antes do casamento = before the marriage
• antes do relacionamento = before the relationship

Since relacionamento is masculine singular and takes the article o, de + o becomes do.

Not always, but very often it does, especially in a sentence like this.

Relacionamento can mean:

• a romantic relationship
• a relationship between people in a broader sense
• even a professional or social relationship, depending on context

In antes do relacionamento, most learners should understand it as before they became a couple.

Yes, absolutely.

A amizade entre elas começou na escola means The friendship between them began at school.

Both are natural, but they feel slightly different:

• A amizade delas = their friendship
• A amizade entre elas = the friendship between them

The second version emphasizes the relationship connecting the two people. The first is a bit more direct and common.

This is a natural Portuguese word order: first the main statement, then extra information about time or context.

• A amizade delas começou na escola = the core message
• antes do relacionamento = extra clarification

It tells us:

1. where it began: na escola
2. when in relation to another stage of life: antes do relacionamento

You could also rearrange parts in Portuguese for emphasis, but this version sounds very normal and clear.

Yes. In many cases, na escola can correspond to either at school or in school, depending on context.

Examples:

• Ela está na escola. = She is at school.
• Eles se conheceram na escola. = They met at school.

In your sentence, na escola most naturally means at school or while they were in school.

A close natural English version would be:

• Their friendship began at school, before the relationship.

Depending on context, English speakers might also say:

• They became friends at school, before they started dating.
• Their friendship started at school, before their relationship began.

The Portuguese sentence is slightly compact and formal in structure, which is very normal.