Hay una fuente en medio de la plaza.

Hay means there is / there are. It is used to say that something exists or is present somewhere.

So:

• Hay una fuente... = There is a fountain...

Spanish often distinguishes between:

• hay = existence: there is / there are
• está / están = location of something specific: is / are

Compare:

• Hay una fuente en medio de la plaza. = There is a fountain in the middle of the square.
• La fuente está en medio de la plaza. = The fountain is in the middle of the square.

In the first sentence, the fountain is being introduced as something that exists there. In the second, it is a specific fountain already known to the speaker and listener.

Una is the indefinite article, meaning a / an.

• una fuente = a fountain

In Spanish, you usually need an article before a singular countable noun, just as in English. So fuente by itself would usually sound incomplete in this kind of sentence.

Also, fuente is a feminine noun, so it takes una, not un.

Spanish nouns have grammatical gender, and fuente is feminine.

That means it uses feminine articles and adjectives:

• la fuente = the fountain
• una fuente = a fountain

There is not always a logical reason from an English point of view. Gender is something you usually learn together with the noun. A good habit is to memorize nouns with their article:

• la fuente, not just fuente

Yes. Fuente most commonly means fountain, especially in a public place like a square.

But depending on context, fuente can also mean:

• source
• spring (of water)
• even font in some contexts, though tipo de letra is also common for font

In this sentence, because of en medio de la plaza, the meaning is clearly fountain.

En medio de means in the middle of.

Literally, it is something like:

• en = in
• medio = middle
• de = of

So:

• en medio de la plaza = in the middle of the square

This is a very common expression in Spanish. You can use it with many places or things:

• en medio de la calle = in the middle of the street
• en medio del parque = in the middle of the park

Because plaza is a feminine noun:

• la plaza = the square

After en medio de, Spanish uses de + article:

• de la plaza = of the square

So the whole phrase is:

• en medio de la plaza = in the middle of the square

If the noun were masculine singular, you would usually get the contraction del:

• en medio del parque = in the middle of the park

But de + la does not contract, so it stays de la.

Yes. In this context, plaza means a town square, public square, or open square in a city or town.

It does not usually mean plaza in the English sense of a shopping area or shopping center. In Spain, plaza very often refers to an open public space.

So la plaza here is best understood as the square.

Spanish often begins existential sentences with hay, just as English often begins with there is / there are.

So the standard structure is:

• Hay + noun + place
• Hay una fuente en medio de la plaza.

This is the most natural neutral order.

You can sometimes move things around for emphasis, for example:

• En medio de la plaza hay una fuente.

That still means the same thing, but now the location is emphasized a bit more.

Yes, absolutely.

Both are correct:

• Hay una fuente en medio de la plaza.
• En medio de la plaza hay una fuente.

The difference is mostly one of focus:

• Hay una fuente en medio de la plaza. = neutral, straightforward
• En medio de la plaza hay una fuente. = emphasizes the location

Spanish word order is often more flexible than English, especially when the meaning stays clear.

You would change the noun phrase to plural:

• Hay fuentes en medio de la plaza. = There are fountains in the middle of the square.
• Hay unas fuentes en medio de la plaza. is possible, but often Spanish simply uses hay + plural noun without unas unless you want to stress some.

Notice that hay stays the same in both singular and plural:

• Hay una fuente... = There is a fountain...
• Hay fuentes... = There are fountains...

That is different from English, where there is and there are change.

Put no before hay:

• No hay una fuente en medio de la plaza. = There isn’t a fountain in the middle of the square.
• More naturally in many contexts: No hay ninguna fuente en medio de la plaza. = There is no fountain in the middle of the square.

Ninguna often sounds more natural than just una in negative sentences when you mean not any / no.

The easiest way is with intonation in speech, or question marks in writing:

• ¿Hay una fuente en medio de la plaza? = Is there a fountain in the middle of the square?

Spanish does not usually need a word-order change like English does. You keep hay in the same place and use intonation or punctuation.

In standard Spanish, hay is pronounced roughly like eye in English.

A simple guide:

• hay ≈ eye

It is a very common word, so it is worth learning well. It comes from the verb haber, but in this existential use you just memorize hay as there is / there are.

In Spain, many speakers pronounce the z in plaza with the th sound from English think:

• plaza ≈ PLA-tha

So in much of Spain:

• Hay una fuente en medio de la plaza sounds roughly like
  eye OO-na FWEN-te en ME-dyo de la PLA-tha

In Latin American Spanish, z is usually pronounced like s, so plaza would sound more like PLA-sa.

Both are correct in their own varieties, but for Spain, the th pronunciation is very common.

Yes: in en medio de, you should learn the whole expression as a chunk.

Although medio by itself can mean middle, half, or even somewhat in other contexts, here the fixed phrase is:

• en medio de = in the middle of

So it is best not to translate word by word every time. Just recognize it as one useful expression.

Sometimes, but not always in exactly the same way.

• en el centro de la plaza = in the center of the square
• en medio de la plaza = in the middle of the square

These are often very similar in meaning. However:

• en medio de is a very common general expression
• en el centro de can sound a bit more geometric or exact

In this sentence, en medio de la plaza is perfectly natural. En el centro de la plaza would also be possible.

A useful way to see it is:

• Hay
  • una fuente
    • en medio de la plaza

So:

1. hay = there is / there are
2. una fuente = a fountain
3. en medio de la plaza = in the middle of the square

This is a very common pattern in Spanish for saying that something exists somewhere:

• Hay un banco en la plaza. = There is a bench in the square.
• Hay una iglesia cerca. = There is a church nearby.
• Hay un coche delante de la casa. = There is a car in front of the house.