Hi ha un cargol a terra, al costat de la galleda que hem posat sota l'aixeta.

Hi ha is the standard Catalan way to say there is or there are.

• Hi ha un cargol = There is a snail / a screw
• literally, hi is a locative element and ha comes from haver

You do not use és here, because és means is in the sense of identifying or describing something:

• És un cargol = It is a snail / screw

And està is used for location or state of something already known:

• El cargol està a terra = The snail / screw is on the ground

So:

• Hi ha... = introducing that something exists or is present
• És... = identifying what something is
• Està... = saying where something is

Catalan usually uses an article with singular countable nouns in this kind of sentence, just like English does.

• un cargol = a snail / a screw

Leaving out the article would sound unnatural here. In existential sentences with hi ha, Catalan normally says:

• Hi ha un llibre sobre la taula
• Hi ha una cadira aquí

So un is simply the indefinite article a / an.

It can mean either, depending on context.

Common meanings of cargol:

• snail
• screw

So this sentence is ambiguous if you see it by itself. Usually the surrounding context tells you which meaning is intended.

For example:

• in a garden or on the floor after rain, cargol probably means snail
• in a workshop or near tools, it may mean screw

Catalan has many words like this where one form has more than one everyday meaning.

A terra means on the ground or on the floor.

It is a fixed expression:

• ser a terra
• caure a terra
• deixar alguna cosa a terra

A useful point for learners: Catalan normally says a terra, without an article here. So it is not usually:

• al terra

Compare:

• Hi ha un cargol a terra = There is a snail / screw on the floor
• El nen seu a terra = The child sits on the floor

Al costat de means next to or beside.

It is made up of:

• a + el = al
• costat = side
• de = of

So literally it is something like at the side of.

Examples:

• al costat de la porta = next to the door
• al costat del cotxe = next to the car

In your sentence:

• al costat de la galleda = next to the bucket

Because Catalan contracts some combinations of preposition + article, but not all.

Common contractions:

• a + el = al
• de + el = del

But with la, Catalan normally does not contract:

• a la
• de la

So:

• al costat = a + el costat
• de la galleda = of the bucket / next to the bucket

That is why you get:

• al costat de la galleda not
• a costat de la galleda and not
• de lа galleda in this case

Galleda means bucket or sometimes pail.

It is a feminine noun, which is why it takes la:

• la galleda

Plural:

• les galledes

Example:

• Hem omplert la galleda d’aigua = We filled the bucket with water

Here que is a relative pronoun, meaning that or which.

So:

• la galleda que hem posat sota l'aixeta means
• the bucket that we put / have put under the tap

Breakdown:

• que = that/which
• hem = we have
• posat = put/placed

So hem posat is the present perfect of posar.

This clause describes la galleda:

• Which bucket?
• The one we put under the tap

Yes, literally hem posat means we have put.

However, in Catalan, especially Central Catalan, the present perfect is often used where English would simply say we put, especially for a completed action connected to the present situation.

So depending on context, English might translate it as:

• the bucket that we have put under the tap
• the bucket that we put under the tap

Both can work.

This is a common point for English speakers: Catalan and English do not always use the perfect tenses in exactly the same way.

Because aixeta is feminine singular:

• la aixeta

But before a vowel sound, la usually becomes l':

• l'aixeta

So:

• sota l'aixeta = under the tap / faucet

This is the same pattern as:

• l'aigua
• l'escola
• l'ampolla

Sota means under or below.

In standard Catalan, sota by itself is perfectly normal:

• sota l'aixeta
• sota la taula

You may also hear sota de in some contexts or varieties, but sota alone is very common and completely correct.

So in this sentence:

• sota l'aixeta = under the tap

Catalan often packs information into one sentence using a relative clause, just like English does.

So instead of saying:

• Hi ha un cargol a terra, al costat de la galleda. Hem posat la galleda sota l'aixeta.

it combines the ideas:

• ...la galleda que hem posat sota l'aixeta

This is natural and efficient. It helps identify which bucket is meant.

English does exactly the same thing:

• the bucket that we put under the tap

The sentence is built like this:

• Hi ha = there is
• un cargol = a snail / screw
• a terra = on the ground / floor
• al costat de la galleda = next to the bucket
• que hem posat sota l'aixeta = that we put / have put under the tap

So the structure is basically:

There is + thing + location + more information about a nearby object

The relative clause que hem posat sota l'aixeta modifies la galleda, not el cargol.

So it means:

• the bucket is the thing we put under the tap
• the snail / screw is the thing on the ground next to that bucket

The infinitive is posar, meaning to put or to place.

Posat is the past participle:

• posar = to put
• he posat = I have put
• hem posat = we have put

Other forms:

• poso = I put / I am putting
• poses = you put
• posa = he/she puts
• posen = they put

So in the sentence, hem posat comes from posar.

The comma separates the main location from extra descriptive information.

Main statement:

• Hi ha un cargol a terra = There is a snail / screw on the ground

Added location detail:

• al costat de la galleda que hem posat sota l'aixeta = next to the bucket that we put under the tap

The comma helps readability and shows a pause, but the sentence would still be understandable without it in many contexts. It mainly organizes the information clearly.