Au milieu du jardin, il y a une petite fontaine.

Both are possible, but they mean slightly different things.

• Dans le jardin = in the garden
• Au milieu du jardin = in the middle of the garden

So au milieu de is a more precise location expression. It tells you the fountain is specifically in the center area, not just somewhere inside the garden.

Au milieu de is a fixed expression meaning in the middle of or amid.

It breaks down like this:

• au = a contraction of à + le
• milieu = middle
• de = of

So au milieu de X literally means at the middle of X, but in natural English we usually say in the middle of X.

Examples:

• au milieu de la rue = in the middle of the street
• au milieu des arbres = in the middle of the trees

Because in French, de + le contracts to du.

So:

• de + le jardin → du jardin

This is a standard contraction in French:

• de + le = du
• de + les = des
• à + le = au
• à + les = aux

So au milieu du jardin is the correct form, not au milieu de le jardin.

Il y a means there is or there are.

In this sentence:

• il y a une petite fontaine = there is a small fountain

This is one of the most common French expressions. It is used to say that something exists or is present somewhere.

Examples:

• Il y a un chat dehors. = There is a cat outside.
• Il y a deux fenêtres. = There are two windows.

Even though il looks like he/it, in il y a you should learn the whole expression as a unit meaning there is / there are.

That is just how the French expression works. Il y a does not change for singular vs. plural.

Compare:

• Il y a une fontaine. = There is a fountain.
• Il y a des fontaines. = There are fountains.

So unlike English, the verb form does not change here. You always use il y a in the present tense.

The comma separates the location phrase from the main clause:

• Au milieu du jardin, = location/topic
• il y a une petite fontaine. = main statement

This is similar to English when we begin with a location phrase:

• In the middle of the garden, there is a small fountain.

The comma helps readability, especially when a sentence starts with a longer introductory phrase. In some cases, French punctuation can be a little flexible, but here the comma is very natural.

Because petit/petite is one of the common adjectives that usually comes before the noun in French.

So:

• une petite fontaine = a small fountain

Many French adjectives come after the noun, but some common ones often come before it, especially adjectives of:

• beauty
• age
• goodness
• size

A helpful memory aid is BAGS:

• Beauty
• Age
• Goodness
• Size

Since petite describes size, it usually goes before the noun.

Because fontaine is a feminine noun.

In French, adjectives usually agree with the noun they describe in gender and number.

• un petit jardin = a small garden
• une petite fontaine = a small fountain

Here:

• fontaine is singular feminine
• so the adjective must also be singular feminine: petite

You usually learn the gender together with the noun:

• une fontaine = a fountain

The article tells you the gender:

• un = masculine singular
• une = feminine singular

Also, many nouns ending in -aine are feminine, though endings are only patterns, not absolute rules. The safest method is to memorize nouns with their article.

So it is better to learn:

• une fontaine rather than just
• fontaine

Yes, absolutely.

Both are correct:

• Au milieu du jardin, il y a une petite fontaine.
• Il y a une petite fontaine au milieu du jardin.

The difference is mainly one of emphasis and flow.

• Starting with Au milieu du jardin puts the location first.
• Starting with Il y a une petite fontaine presents the fountain first, then says where it is.

French often moves a location phrase to the front for emphasis or style.

They are very close, but not always exactly identical.

• au milieu du jardin = in the middle of the garden
• au centre du jardin = in the center of the garden

In many contexts, they can be used almost interchangeably. But:

• milieu can feel a little more general or spatial
• centre can sound a little more geometric or precise

In this sentence, either could work, but au milieu du jardin sounds very natural and descriptive.

Yes, this is a very common pronunciation issue.

Il y a is usually pronounced roughly like:

• eel ya

The l in il links smoothly into y a, so the whole expression often sounds like one chunk.

A slow breakdown:

• il → eel
• y → like ee
• a → ah

But in normal speech, you should think of it as one expression:

• il y a → eel ya

This is one reason it is best to memorize il y a as a set phrase.