O sofá está ao lado da janela.

Because Portuguese usually uses estar for location.

• estar = to be, in a place or condition
• ser = to be, for identity, characteristics, origin, time, etc.

So:

• O sofá está ao lado da janela. = The sofa is next to the window.
• Not O sofá é ao lado da janela.

A simple learner rule is:

• use estar for where something is
• use ser for what something is

Ao lado de means next to, beside, or at the side of.

It is a very common location expression.

Examples:

• ao lado da janela = next to the window
• ao lado da porta = next to the door
• ao lado do carro = next to the car

Literally, lado means side, so the phrase is something like at the side of.

Because the full expression is ao lado de.

It works as a set phrase:

• ao lado de
  • noun

So you say:

• ao lado da janela
• ao lado do sofá
• ao lado da cama

You normally do not say just lado da janela to mean next to the window.

Ao is a contraction of:

• a + o = ao

Here, it appears because of the expression ao lado.

You can think of it like this:

• a = to / at
• o lado = the side

So:

• ao lado = at the side

This kind of contraction is very common in Portuguese.

Other examples:

• ao mercado = to the market
• ao redor = around

Because Portuguese contracts de + a into da.

So:

• de + a = da
• de + o = do

In this sentence:

• da janela = de + a janela

This happens all the time:

• ao lado da porta
• perto do carro
• embaixo da mesa

So de a janela is not the normal form; da janela is.

Portuguese uses definite articles very often, often more than English does.

Here:

• o sofá = the sofa
• a janela = the window

In Portuguese, nouns are commonly used with articles when talking about specific things. So even where English might sometimes sound natural without an article, Portuguese often still uses one.

That is why janela appears as a janela, and after contraction, da janela.

Yes, sofá is masculine:

• o sofá

Its gender is shown by the article o, not just by the ending.

This is important because noun endings do not always reliably tell you the gender. Many masculine nouns do end in -o, and many feminine nouns do end in -a, but there are lots of exceptions.

So the safest habit is to learn nouns together with their article:

• o sofá
• a janela

Because janela is a feminine noun:

• a janela

That is why the sentence has:

• da janela = de + a janela

Again, it helps to memorize nouns with their article:

• a janela
• a porta
• a mesa

The word order is very similar to English:

• O sofá = subject
• está = verb
• ao lado da janela = location phrase

So the structure is:

• Subject + verb + place

This makes the sentence fairly straightforward for English speakers.

Yes, but it is not exactly the same.

• ao lado da janela = next to / right beside the window
• perto da janela = near the window

So if the sofa is directly beside the window, ao lado da janela is better. If it is just somewhere close to the window, perto da janela works.

Sofá is pronounced roughly like soh-FAH.

Important points:

• the stress is on the last syllable: fa
• the accent mark (á) shows that stress

So not SO-fa, but so-FA

The accent in está shows the stressed syllable.

• está = es-TAH

It also helps distinguish it from other forms and follows Portuguese spelling rules.

For learners, the most practical thing is:

• pronounce it with stress on the second syllable
• es-TAH

In Brazilian Portuguese, janela is roughly:

• zhah-NEH-lah

A few pronunciation notes:

• j in Brazilian Portuguese sounds like the s in measure or the zh sound
• the stress is on ne
• final a is usually a light ah sound

So:

• ja-NE-la with the stress in the middle

Yes. Portuguese allows some flexibility, especially for emphasis.

For example:

• O sofá está ao lado da janela.
• Ao lado da janela está o sofá.

The first one is the most neutral and natural for a learner to use. The second sounds more literary or emphatic, as if highlighting the location first.

So for everyday use, stick with:

• O sofá está ao lado da janela.

A helpful breakdown is:

• O = the
• sofá = sofa
• está = is
• ao lado de = next to / at the side of
• a janela = the window

With contractions:

• ao = a + o
• da = de + a

So the sentence is literally something like:

• The sofa is at the side of the window

And naturally in English:

• The sofa is next to the window.