Hi ha una porta a l'habitació.

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

It is made of:

• ha: the he/she/it has form of haver
• hi: a little word that is part of the fixed existential expression haver-hi

So learners often treat hi ha as one chunk meaning there is / there are.

Because for existence, Catalan normally uses haver-hi, not plain haver.

So:

• Hi ha una porta = There is a door
• Ha una porta is not correct for this meaning

The hi is not optional here. In this structure, it belongs to the expression.

In standard Catalan, existential hi ha stays the same whether the noun is singular or plural.

For example:

• Hi ha una porta = There is a door
• Hi ha dues portes = There are two doors

So unlike English, Catalan does not normally change from is to are in this structure.

Una porta uses the indefinite article, so it introduces a door, not a specific door already known to the listener.

Use:

• una porta for a door
• la porta for the door

So Hi ha una porta a l'habitació presents the door as something being mentioned for the first time, or as an unspecified door.

Yes. Porta is a feminine noun in Catalan, so it takes feminine articles:

• una porta = a door
• la porta = the door

If it were a masculine noun, you would use un or el instead.

In Catalan, a can often mean to, but it is also very commonly used for location, where English might use in, at, or sometimes to depending on context.

So in this sentence:

• a l'habitació means in the room

This is very normal Catalan. It is best not to match a to just one English preposition.

Because the article la becomes l' before a word that begins with a vowel or a silent h.

So:

• la habitació becomes l'habitació

The h in habitació is silent, so elision happens.

Yes. A l'habitació hi ha una porta is perfectly natural.

Both are correct:

• Hi ha una porta a l'habitació
• A l'habitació hi ha una porta

The second version puts the location first, which can sound more natural in many contexts if you want to set the scene first.

Use hi ha when you are saying that something exists or is present somewhere.

• Hi ha una porta a l'habitació = a door exists/is present in the room

Use és or està when you are talking about a specific thing rather than introducing it.

For example:

• La porta està oberta = The door is open
• La porta és blanca = The door is white

So hi ha is for existence/presence, while és/està describe or locate something more specifically.

A simple approximate pronunciation is:

ee AH OO-nuh POR-tuh uh luh-bee-tuh-see-OH

A few useful notes:

• hi sounds like ee
• the h in ha and habitació is silent
• habitació is stressed on the last syllable: -ció

A more Catalan-like pronunciation will vary a little by dialect, but those points will help a lot.