Aquesta és una bona oportunitat.

Because oportunitat is a feminine singular noun, and the demonstrative has to agree with it.

• aquest = this (masculine singular)
• aquesta = this (feminine singular)
• aquests = these (masculine plural)
• aquestes = these (feminine plural)

Since oportunitat is feminine, you say aquesta oportunitat.

És is the 3rd person singular form of the verb ser (to be).

So:

• és = is

In Aquesta és una bona oportunitat, it links the subject aquesta (this) with the description una bona oportunitat (a good opportunity).

The accent in és helps distinguish it from es.

• és = is
• es = a pronoun, often meaning something like oneself, to oneself, or part of a pronominal verb

So the accent is important both for spelling and meaning.

Yes. Una is simply the feminine singular indefinite article, the equivalent of English a/an.

Catalan articles agree with gender and number:

• un = a/an (masculine singular)
• una = a/an (feminine singular)

Because oportunitat is feminine, you need una:

• una oportunitat

Because adjectives in Catalan usually agree with the noun they describe in gender and number.

The adjective here is bo / bona (good):

• bo = masculine singular
• bona = feminine singular
• bons = masculine plural
• bones = feminine plural

Since oportunitat is feminine singular, the correct form is bona.

That is a very good question. In Catalan, many adjectives do come after the noun, but some very common descriptive adjectives—especially ones expressing an evaluation, like bo / bona—can often come before the noun.

So:

• una bona oportunitat = a good opportunity

This sounds natural and very common. Putting bona before the noun often gives it a smooth, idiomatic feel.

It is grammatically possible, but it sounds less natural in this context.

• una bona oportunitat is the normal, idiomatic choice
• una oportunitat bona is much less common and may sound more marked or contrastive

In everyday Catalan, Aquesta és una bona oportunitat is the best version.

Here aquesta is being used as a demonstrative pronoun, not just a demonstrative adjective.

Compare:

• Aquesta oportunitat és bona.
  = This opportunity is good.
  Here aquesta modifies the noun directly.

• Aquesta és una bona oportunitat.
  = This is a good opportunity.
  Here aquesta stands alone and means this.

So in your sentence, aquesta works like English this by itself.

Yes, but it is not exactly the same.

• Aquesta usually refers to a specific feminine thing already understood from context
• Això means this / this thing in a more neutral, general way

So:

• Aquesta és una bona oportunitat = This one / this (feminine thing) is a good opportunity
• Això és una bona oportunitat = This is a good opportunity

Both are possible, but aquesta is more specifically tied to a feminine referent.

A practical approximate pronunciation is:

ah-KES-tuh ez OO-nuh BO-nuh oo-por-too-nee-TAT

A few notes:

• aquesta: stress on ques
• és: a clear ez sound
• una: often sounds like OO-nuh
• bona: stress on bo
• oportunitat: stress on the last syllable, -tat

The final t in oportunitat is pronounced.

Very often, yes. Many Catalan nouns ending in -tat are feminine, similar to English nouns ending in -ty and Romance-language patterns like -dad or -té.

Examples:

• la ciutat = the city
• la veritat = the truth
• la oportunitat / oportunitat = opportunity

So oportunitat is feminine, and that affects:

• aquesta
• una
• bona

It uses ser: és.

Catalan, like Spanish, often distinguishes between ser and estar. Here you use ser because the sentence identifies or classifies something:

• This is a good opportunity.

You are saying what something is, not describing a temporary location or condition. So ser is the correct verb.

Almost completely:

• Aquesta = this
• és = is
• una = a
• bona = good
• oportunitat = opportunity

So the structure is very close to English: This is a good opportunity.

The main thing to remember is that Catalan shows gender agreement in several words, which English does not.