Ispod prozora je sto, a iznad stola je velika fotografija planine.

Because they are in the genitive case.

In the sentence:

• ispod prozora = below the window
• iznad stola = above the table
• fotografija planine = a photograph of a mountain

The basic forms are:

• prozor = window
• sto = table
• planina = mountain

Their genitive singular forms are:

• prozora
• stola
• planine

So a very important pattern here is that certain prepositions and noun relationships require the genitive.

Yes, in normal usage ispod (below / underneath) and iznad (above) take the genitive.

So you get:

• ispod prozora = below the window
• iznad stola = above the table

This is true whether you are describing position or movement in standard Serbian. So if you learn ispod and iznad, it is best to learn them together with the rule + genitive.

This is because je is a clitic in Serbian, and clitics usually go in second position in the sentence or clause.

In the clause:

• Ispod prozora je sto

the first unit is Ispod prozora, and then the clitic je comes right after it.

So Serbian often structures sentences like this:

• [place] + je + [thing]

Literally:

• Below the window is a table

Natural English usually says:

• There is a table below the window

So the Serbian word order is normal and natural.

Both patterns are possible, but they do not sound exactly the same.

• Ispod prozora je sto focuses first on the location
• Sto je ispod prozora focuses first on the table

The version in your sentence is a very common way to describe what is where in a room, picture, or scene. It is similar to English:

• Below the window, there is a table

So this word order is especially natural in descriptions.

Here a means something like and, while, or and then / whereas, depending on context.

In this sentence:

• Ispod prozora je sto, a iznad stola je velika fotografija planine.

it connects two related pieces of information:

• below the window there is a table
• above the table there is a large photograph of a mountain

So a is not just a plain joining word like i (and). It often introduces a second statement that is parallel, contrasted, or added from another angle.

Here it feels very natural because the sentence is describing two spatial relationships.

Because the adjective velika (big / large) must agree with the noun fotografija in:

• gender
• number
• case

Fotografija is:

• feminine
• singular
• nominative here, because it is the subject of je

So the adjective also has to be:

• feminine singular nominative → velika

That is why you get:

• velika fotografija = a large photograph

Because Serbian commonly uses the genitive after a noun to express of.

So:

• fotografija planine = photograph of a mountain

Here:

• fotografija = photograph
• planine = of a mountain

This is a very common structure in Serbian:

• čaša vode = a glass of water
• vrata kuće = the door of the house
• slika grada = a picture of the city

So planine is genitive singular, showing the relationship of a mountain.

Because Serbian does not have articles like English a/an and the.

So:

• sto can mean a table or the table
• prozor can mean a window or the window
• fotografija can mean a photograph or the photograph

Which meaning is intended depends on context.

In your sentence, English naturally uses:

• Below the window is a table, and above the table is a large photograph of a mountain.

But Serbian does not need separate words for those articles.

In standard Serbian, sto is the normal word for table.

Learners often notice stol because:

• stol exists in some neighboring varieties, especially Croatian
• Serbian normally uses sto

So in Serbian:

• sto = table
• stolica = chair

Also, sto is a masculine noun, even though it ends in -o, which can surprise learners.

Its forms include:

• nominative: sto
• genitive: stola

That is why the sentence has iznad stola.

Yes. Je is the 3rd person singular present form of biti (to be).

So:

• je = is

In this sentence it is used twice:

• Ispod prozora je sto = There is a table below the window
• iznad stola je velika fotografija planine = Above the table is a large photograph of a mountain

Serbian often uses to be in this way to state that something exists in a certain place.

Yes, absolutely. That is actually very close to the Serbian structure.

A more literal translation is:

• Below the window is a table, and above the table is a large photograph of a mountain.

A more natural everyday English translation might be:

• There is a table below the window, and above the table there is a large photograph of a mountain.

Both are correct. The Serbian sentence is organized around location first.

Yes, Serbian word order is fairly flexible, though the emphasis changes.

For example, you could say:

• Sto je ispod prozora, a velika fotografija planine je iznad stola.

This still communicates the same basic facts, but it sounds more like you are talking specifically about the table and the photograph.

The original:

• Ispod prozora je sto, a iznad stola je velika fotografija planine

is especially natural for describing a scene.

So the meaning stays similar, but the focus and style shift.

Both can relate to something being lower than something else, but they are not exactly the same.

• ispod = below / underneath
• pod = under, often with a stronger idea of being directly under or physically beneath something

So:

• ispod prozora = below the window
• pod stolom = under the table

Also, pod usually takes the instrumental for location:

• pod stolom = under the table

while ispod takes the genitive:

• ispod stola = below the table

In your sentence, ispod prozora is the natural choice because it simply describes a position lower than the window.