El gos és al parc.

A simple approximation is el goss ess al park.

A few helpful details:

• gos does not sound like English goes. It is closer to goss.
• és sounds like ess with a clear e.
• parc ends in a hard k sound.

Regional pronunciation varies, but that approximation is good for a beginner.

El is the masculine singular definite article, so it means the.

So:

• el gos = the dog

Compare:

• un gos = a dog
• la gossa = the female dog
• els gossos = the dogs

És is the 3rd person singular form of the verb ser, which usually means to be.

So:

• jo sóc = I am
• tu ets = you are
• ell/ella és = he/she is

In this sentence, és means is.

The accent in és is important.

It helps:

1. mark the stressed vowel in the word
2. distinguish it from es, which is a different word, usually a reflexive or passive pronoun

So:

• és = is
• es = a pronoun, as in es renta = he/she washes himself/herself

Because a + el contracts to al in Catalan.

So:

• a + el parc → al parc

This is a very common contraction.

Another common one is:

• de + el → del

Examples:

• Va al parc = He/She goes to the park
• Ve del parc = He/She comes from the park

Because Catalan and English do not match word-for-word in their prepositions.

In Catalan, a is very often used for location where English might use at or in.

So:

• al parc can mean at the park or in the park, depending on context.

For a learner, the safest thing is to learn al parc as the normal Catalan phrase here.

Sometimes yes, but al parc is the most natural and standard choice in this sentence.

Catalan can use both a and en with places in some contexts and varieties, but:

• És al parc is the safest form to learn first.

So if you are unsure, use al parc here.

Yes, you may hear El gos està al parc, and in everyday speech it is very common.

Broadly speaking:

• és al parc = simple location
• està al parc = also location, often with a sense of current or temporary presence

For a beginner, it is enough to know that both can appear, but the sentence you were given, El gos és al parc, is correct.

Yes, in this sentence the basic order is very similar to English:

• El gos = the dog
• és = is
• al parc = at/in the park

So the structure is:

subject + verb + place

That is the normal, neutral order here.

Because Catalan often does not need subject pronouns.

The subject is already expressed by el gos, so adding a pronoun would be unnecessary.

Catalan commonly leaves out pronouns when the subject is already clear:

• És al parc = He/She/It is at the park
• El gos és al parc = The dog is at the park

English usually needs a subject pronoun, but Catalan often does not.

You change the article, the noun, and sometimes the verb.

Examples:

• La gossa és al parc = The female dog is at the park
• Els gossos són al parc = The dogs are at the park
• Les gosses són al parc = The female dogs are at the park

Notice:

• singular és = is
• plural són = are

Then Catalan often uses elision.

Examples:

• L'home és al parc = The man is at the park
• El gos és a l'escola = The dog is at the school

So instead of al escola, you get a l'escola.

That is because the article changes before a vowel:

• el / la → often l' before a vowel sound