A estufa é capaz de proteger os rebentos.

They are definite articles: a = the for a feminine singular noun, and os = the for a masculine plural noun.

• a estufa = the greenhouse
• os rebentos = the shoots / sprouts

In Portuguese, articles are used very often, more often than in English. You usually need them before nouns when talking about specific things.

Here:

• estufa is feminine singular, so it takes a
• rebentos is masculine plural, so it takes os

In Portuguese, nouns have grammatical gender, and estufa is a feminine noun. That is why it goes with:

• a estufa
• not o estufa

There is no perfect rule for gender, but many nouns ending in -a are feminine. This is a common pattern, though there are exceptions in Portuguese.

É capaz de + infinitive means is capable of + -ing or can in the sense of having the ability to do something.

So:

• A estufa é capaz de proteger os rebentos. = The greenhouse is capable of protecting the shoots. = more naturally in English, The greenhouse can protect the shoots.

You could also say:

• A estufa pode proteger os rebentos.

That also means The greenhouse can protect the shoots, but é capaz de emphasizes capacity/ability, while pode is the more direct everyday word for can / may.

Because the pattern is:

• ser capaz de + infinitive

So you say:

• é capaz de proteger
• sou capaz de fazer
• somos capazes de ajudar

The de is just part of the normal structure. It is not optional here.

A good way to memorize it is as one chunk:

• ser capaz de

Because after é capaz de, Portuguese uses the infinitive form of the verb:

• é capaz de proteger
• é capaz de ajudar
• é capaz de crescer

This is similar to English capable of protecting, except Portuguese uses de + infinitive, not a form like protecting.

So:

• proteger = to protect

Rebentos usually means shoots, sprouts, or young plant growth.

Singular:

• rebento

Plural:

• rebentos

In a gardening or farming context, it refers to new growth coming out of a plant. Depending on context, English might translate it as:

• shoots
• sprouts
• new shoots

Good question. Capaz does agree in number, but in this sentence it stays capaz because the subject is singular:

• A estufa é capaz de... = singular

If the subject were plural, it would become:

• As estufas são capazes de proteger os rebentos.

So:

• singular: capaz
• plural: capazes

For gender, capaz has the same form in masculine and feminine singular:

• o rapaz é capaz
• a rapariga é capaz

É is the 3rd person singular of the verb ser (to be):

• eu sou
• tu és
• ele/ela é

Here it matches a estufa (the greenhouse), which is singular:

• A estufa é capaz de... = The greenhouse is capable of...

So é means is.

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

• é = is
• e = and

So the accent is important because it changes the word completely.

Examples:

• A estufa é grande. = The greenhouse is big.
• A estufa e o jardim... = The greenhouse and the garden...

This is the normal, neutral word order in Portuguese:

• A estufa = subject
• é capaz de proteger = verb phrase
• os rebentos = object

Portuguese usually follows Subject + Verb + Object, just like English.

You can change the order in some contexts for emphasis, but this version is the most natural and standard one for learners.

A rough pronunciation guide for European Portuguese is:

• A estufa é capaz de proteger os rebentos
• roughly: uh shtoo-fuh eh kuh-pash duh pro-te-zher ooz ruh-bẽ-toosh

A few useful points for European Portuguese:

• estufa often sounds closer to shtufa than estufa with a full English-style e
• final unstressed vowels are often reduced
• de is often a weak sound, like du/də
• s at the end of a word often sounds like sh in European Portuguese

This is only approximate, but it helps you avoid reading it too much like English spelling.

The grammar would still be correct in Brazilian Portuguese:

• A estufa é capaz de proteger os rebentos.

But vocabulary preferences may differ. In Brazil, rebentos is understandable, but in everyday plant-related language people might more often use words like:

• brotos
• sometimes other context-specific terms

So in European Portuguese, rebentos feels very natural in this context.

You would change the subject, the verb, the article, and capaz:

• As estufas são capazes de proteger os rebentos.

Changes:

• a → as
• estufa → estufas
• é → são
• capaz → capazes

The object os rebentos stays plural as it already is.

So this means:

• The greenhouses are capable of protecting the shoots.