Ele é um verdadeiro amigo.

Because é is the he/she/it is form of the verb ser. The accent marks the stressed vowel and also helps distinguish it from e, which means and.

In European Portuguese, é is pronounced with an open e sound.

Yes, very often.

Portuguese is a pro-drop language, so subject pronouns are often omitted when the meaning is clear from the verb form or the context. Since é already tells you it is he/she/it is, you can often simply say:

É um verdadeiro amigo.

That said, Ele is perfectly fine here and may be used for emphasis, contrast, or clarity.

Because ser is used for qualities seen as more essential, lasting, or defining.

In this sentence, calling someone um verdadeiro amigo describes what kind of person he is, not a temporary state. So ser is the natural choice.

Using estar here would sound wrong in normal Portuguese.

Because amigo is a singular countable noun, and in this kind of sentence Portuguese normally uses the indefinite article um.

So:

Ele é um verdadeiro amigo.

sounds natural.

If you removed um, the sentence would sound unnatural in modern standard Portuguese.

Adjective position in Portuguese can affect nuance.

In um verdadeiro amigo, putting verdadeiro before the noun gives an emphatic sense like a real / genuine / true friend. It highlights the idea that he really deserves to be called a friend.

If you say um amigo verdadeiro, it can sound more descriptive and sometimes more literal, closer to a sincere / truthful friend. In many contexts both are possible, but um verdadeiro amigo is the more natural choice for the usual meaning of a true friend.

Yes. Adjectives in Portuguese agree with the noun in gender and number.

Here, amigo is masculine singular, so we use verdadeiro.

Other forms:

• masculine singular: verdadeiro amigo
• feminine singular: verdadeira amiga
• masculine plural: verdadeiros amigos
• feminine plural: verdadeiras amigas

So for a woman, you would say:

Ela é uma verdadeira amiga.

A rough European Portuguese pronunciation is:

Ele é um verdadeiro amigo
EH-luh eh oong vur-duh-DAI-roo uh-MEE-goo

A few useful notes:

• Ele is often reduced in fast speech, especially the final vowel.
• um has a nasal sound.
• In European Portuguese, unstressed vowels are often reduced, so the sentence may sound more compressed than a learner expects.

A more phonetic approximation would be:

[ˈɛlɨ ɛ ũ vɨɾdɐˈðɐjɾu ɐˈmiɣu]

You need to change the pronoun, article, noun, and adjective as needed.

Examples:

• Ela é uma verdadeira amiga.
• Eles são verdadeiros amigos.
• Elas são verdadeiras amigas.

Notice:

• ele / ela / eles / elas
• é / são
• um / uma
• amigo / amiga / amigos / amigas
• verdadeiro / verdadeira / verdadeiros / verdadeiras

Yes.

Um amigo simply means a friend.
Um verdadeiro amigo adds emphasis: it suggests someone is a genuine, loyal, or real friend, not just a casual acquaintance or someone who only seems friendly.

So the sentence is slightly warmer and more expressive than just Ele é um amigo.