La fiança i les despeses són al contracte.

Because fiança is singular feminine, so it takes la.
Despeses is plural feminine, so it takes les.

• la fiança = the deposit
• les despeses = the expenses / the fees / the costs

Catalan articles must agree in gender and number with the noun.

Because the subject is plural: La fiança i les despeses.

Even though fiança is singular and despeses is plural, together they form a compound subject, so the verb must be plural.

• és = is
• són = are

So:

• La fiança és... = The deposit is...
• La fiança i les despeses són... = The deposit and the expenses are...

Catalan often uses ser for location when talking about where something appears, is stated, or is contained, especially in texts, documents, events, or fixed contexts.

So són al contracte means they are included in / appear in the contract.

Using estar would sound less natural here.
With documents and written content, ser is very common.

Al is a contraction of a + el.

• a = to / at / in
• el = the
• al = to the / at the / in the

So al contracte literally means something like in the contract or on the contract, depending on context. In natural English here, it would usually be understood as in the contract.

Because Catalan usually uses the definite article with nouns like this.

So you say:

• al contracte = in the contract

not usually:

• a contracte

The article el is needed, and when a comes before el, they combine into al.

Fiança usually means deposit, especially a security deposit, such as in a rental context.

For example, in housing or rentals:

• la fiança = the security deposit

Depending on context, it can also have legal or financial meanings related to a guarantee or bond, but for many learners the most useful meaning is deposit.

Despeses means expenses, costs, or fees.

It is very often used in the plural because people usually talk about multiple costs together.

Examples:

• les despeses = the expenses / the costs
• despeses addicionals = additional costs

There is also singular despesa, meaning expense, but in many everyday situations the plural is more common.

Because contracte is a masculine noun in Catalan, so it takes el in the singular:

• el contracte = the contract

That is why a + el contracte becomes al contracte.

This is something that has to be learned with the noun, since grammatical gender does not always match English.

In this sentence, it is best understood as in the contract.

With documents, Catalan often uses a where English prefers in:

• És al contracte = It is in the contract
• És a la llista = It is on the list / in the list

So the exact English preposition can vary, but the Catalan structure is normal.

This is a normal and natural word order in Catalan:

La fiança i les despeses són al contracte.

It follows the basic pattern:

subject + verb + place/complement

You could change the order for emphasis, for example:

Al contracte hi són la fiança i les despeses.

But that is more marked. For a learner, the original sentence is the standard and easiest pattern to use.

Because it is not necessary here.

Catalan can use hi to refer to a place or location, but when the location is already stated directly as al contracte, the sentence works perfectly without it:

• La fiança i les despeses són al contracte.

If you wanted to emphasize or restructure the sentence, hi could appear in other versions, but it is not needed in this straightforward form.