A amizade delas é importante.

A is the feminine singular definite article, meaning the.

It appears here because amizade is a feminine singular noun:

• a amizade = the friendship

In Portuguese, using the definite article is very common, even in places where English might sometimes leave it out.

Delas means of them or theirs, referring to a feminine plural group.

So:

• a amizade delas = their friendship
• literally: the friendship of them

It is used when the people being referred to are all female, or when the pronoun refers back to feminine plural nouns.

Because delas is the feminine plural form, while deles is the masculine/mixed plural form.

• delas = of them, referring to women/girls or feminine plural nouns
• deles = of them, referring to men/boys or a mixed group

So if the friendship belongs to two or more women or girls, delas is the correct choice.

Both can sometimes express possession, but delas is often clearer.

• a amizade delas = their friendship
• a sua amizade could mean your friendship, his friendship, her friendship, or even their friendship, depending on context

Because seu/sua/seus/suas can be ambiguous in Portuguese, speakers often prefer dele/dela/deles/delas to make the meaning explicit.

So a amizade delas clearly means the friendship belonging to them.

Because amizade is a feminine noun in Portuguese.

You can tell from the article:

• a amizade

This is something you generally have to learn with the noun. While many nouns ending in -ade are feminine, it is best to learn nouns together with their article:

• a amizade
• a cidade
• a verdade

Because importante is an adjective with the same form for both masculine and feminine in the singular.

So you get:

• o livro é importante
• a amizade é importante

It does change in the plural:

• o livro é importante
• os livros são importantes
• a amizade é importante
• as amizades são importantes

É is the third-person singular form of the verb ser in the present tense:

• eu sou
• você/ele/ela é
• nós somos
• eles/elas são

The subject of the sentence is a amizade delas, which is singular because the main noun is amizade.

So even though delas refers to more than one person, the subject is still friendship—one friendship—so the verb must be singular:

• A amizade delas é importante.

The accent in é helps distinguish it from e, which means and.

• é = is
• e = and

So the accent is important for meaning.

Example:

• Ela é minha amiga. = She is my friend.
• Ela e minha amiga... = This would mean something different and sounds incomplete/wrong in this context.

A natural Brazilian pronunciation is approximately:

a mee-zah-JEE dah-lahs eh eem-por-TAHN-chee

A few notes:

• amizade has stress on the last syllable: amiZADE
• delas sounds roughly like DE-las
• é is a clear open eh
• importante often sounds like imporTANte, with the final te in Brazil often sounding like chee in many accents

Pronunciation varies by region, but that approximation is a good start.

In standard Portuguese, that sounds unnatural here.

The normal form is:

• A amizade delas é importante.

Portuguese usually prefers the article in this kind of sentence, especially when talking about a specific concept or relationship.

Yes. A amizade entre elas é importante is also correct, but it has a slightly different feel.

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

The first one focuses more on possession or association.
The second one emphasizes the relationship connecting them.

In many contexts, both work well.

Yes, but the most neutral order is:

• A amizade delas é importante.

You may also see:

• É importante a amizade delas.

This version is grammatical, but it sounds more marked or stylistic, with emphasis on important.

What you cannot do is remove the verb:

• A amizade delas importante ❌

Portuguese needs the verb é here.

Then you would use dela instead of delas:

• A amizade dela é importante. = Her friendship is important.

Compare:

• dela = of her
• delas = of them (feminine plural)

And if it were a masculine or mixed group:

• A amizade deles é importante. = Their friendship is important.