Al pati hi ha un arbre gran que fa molta ombra a l'estiu.

Al pati means in the patio / in the courtyard.

Catalan often puts the place first when introducing what exists somewhere. So:

• Al pati hi ha... = In the patio, there is...

This word order is very natural in Catalan. English can do this too, but English more often says There is a big tree in the patio.

Also, al is a contraction:

• a + el = al

So:

• el pati = the patio / courtyard
• al pati = in/to the patio, depending on context

Here it means location: in the courtyard.

Hi ha means there is or there are.

It is one of the most common Catalan expressions for existence:

• Hi ha un arbre = There is a tree
• Hi ha dos arbres = There are two trees

Even though ha looks like a form of haver, you should learn hi ha as a fixed expression meaning there is/are.

In hi ha, hi is a locative pronoun, historically connected with the idea of there.

For a learner, the easiest approach is:

• learn hi ha as a whole expression = there is / there are

You do not usually translate hi separately in this phrase. It is just part of the standard Catalan way to say that something exists somewhere.

So in this sentence:

• Al pati hi ha un arbre gran
  = There is a big tree in the courtyard

In Catalan, adjectives often come after the noun:

• un arbre gran = a big tree
• una casa petita = a small house

That is the most neutral, ordinary order.

Catalan can sometimes place certain adjectives before the noun, but that often changes the tone or emphasis. For everyday description, noun + adjective is the normal pattern.

So:

• un arbre gran is the standard way to say a big tree

Here que means that or which and introduces a relative clause.

It refers back to un arbre gran:

• un arbre gran que fa molta ombra
• a big tree that gives a lot of shade

So the structure is:

• un arbre gran = the noun
• que fa molta ombra = extra information about that noun

Catalan uses que very often in this way, just like English uses that or which.

Yes, literally fa molta ombra is something like makes a lot of shade.

In Catalan, fer ombra is the normal expression for to cast shade / to provide shade.

So:

• L'arbre fa ombra = The tree gives/casts shade
• L'arbre fa molta ombra = The tree gives a lot of shade

This is very natural Catalan, even though English uses different verbs.

Because ombra is a feminine singular noun, and molt must agree with it.

Agreement forms:

• molt = masculine singular
• molta = feminine singular
• molts = masculine plural
• moltes = feminine plural

Since:

• ombra is feminine singular

we get:

• molta ombra = a lot of shade

Compare:

• molt sol = a lot of sun
• molta pluja = a lot of rain

A l'estiu means in summer or in the summer.

There are two things happening here:

1. a is the preposition used in many time expressions.
2. l' is the article el or la shortened before a vowel.

So:

• el estiu becomes l'estiu
• a + l'estiu = a l'estiu

This apostrophe is used because estiu begins with a vowel.

They are related, but you should not assume they match perfectly in every context.

Pati usually means:

• courtyard
• yard
• playground
• sometimes patio, depending on context

So Al pati could be:

• In the courtyard
• In the yard
• In the patio

The best translation depends on the situation. If this is a house, courtyard or yard may sound more natural than patio.

Because molta ombra is an indefinite quantity expression, similar to a lot of shade in English.

Catalan often omits the article after quantity words like:

• molt / molta
• poc / poca
• massa
• prou

So:

• fa molta ombra = it gives a lot of shade

You would not normally say fa la molta ombra.

Yes. That is also correct.

Compare:

• Al pati hi ha un arbre gran...
• Hi ha un arbre gran al pati...

Both are grammatical. The difference is mainly emphasis and information structure.

• Al pati hi ha... puts the location first: As for the courtyard, there is...
• Hi ha... al pati starts with the existence statement first: There is... in the courtyard

The original version sounds very natural because it sets the scene first.

Because apostrophes in Catalan depend on the word before the noun.

• el estiu becomes l'estiu because the definite article el drops its vowel before a vowel sound.
• un arbre stays un arbre because the indefinite article un does not apostrophize here.

So:

• l'estiu
• l'arbre would also be correct for the tree
• but un arbre remains unchanged

No, in normal reading it describes un arbre gran.

That is because que usually attaches to the noun phrase immediately before it:

• un arbre gran que fa molta ombra a l'estiu

So the meaning is:

• a big tree that gives a lot of shade in summer

It does not mean that the courtyard gives shade. The tree is clearly the thing doing that.

You would change the noun and any words that agree with it:

• Al pati hi ha uns arbres grans que fan molta ombra a l'estiu.

Changes:

• un arbre → uns arbres
• gran → grans
• fa → fan

But molta ombra stays singular because shade is still being treated as an uncountable thing.

So:

• There are some big trees in the courtyard that give a lot of shade in summer.