Ovo sedište je slobodno.

Because sedište is a neuter noun, and the demonstrative this has to agree with it.

In Serbian:

• ovaj = this, for masculine nouns
• ova = this, for feminine nouns
• ovo = this, for neuter nouns

So:

• ovaj sto = this table
• ova stolica = this chair
• ovo sedište = this seat

The form ovo matches the gender of sedište.

A very common clue is the ending. Many Serbian nouns ending in -e or -o are neuter.

Since sedište ends in -e, it is neuter, so other words referring to it must also be neuter:

• ovo sedište
• slobodno sedište
• to sedište

This is why both ovo and slobodno also appear in neuter form.

Je is the 3rd person singular present form of the verb biti = to be.

So in Ovo sedište je slobodno, je means is.

Compare:

• ja sam = I am
• ti si = you are
• on/ona/ono je = he/she/it is

Unlike in some Slavic languages, Serbian normally does use the present-tense form of to be in sentences like this.

In normal standard Serbian, no. You would usually keep it:

• Ovo sedište je slobodno.

Leaving out je would sound incomplete or unnatural in standard speech.

Serbian can sometimes omit forms of to be in very specific styles, headlines, or colloquial expressions, but not in a basic sentence like this one.

Because slobodno is an adjective, and it must agree with sedište in gender, number, and case.

Since sedište is:

• neuter
• singular
• nominative

the adjective must also be:

• neuter
• singular
• nominative

So you get slobodno.

Compare:

• slobodan čovek = a free man / available man
• slobodna stolica = a free chair
• slobodno sedište = a free seat

Here it means available / unoccupied.

That is a very common use of slobodan / slobodna / slobodno in Serbian. In context, it often means:

• not taken
• empty
• available

For example:

• Da li je ovo mesto slobodno? = Is this seat/place free?
• Soba je slobodna. = The room is available.

So the idea is not political freedom here, but that nobody is using the seat.

Yes. Mesto is often used for place or spot, and in many situations it can sound very natural.

Difference in nuance:

• sedište = the actual seat itself
• mesto = the place/spot, often where someone sits

On a bus, train, or in a theater, both can work depending on context.
Sedište focuses more on the physical seat.
Mesto is a bit broader.

The most natural neutral order is:

• Ovo sedište je slobodno.

Serbian word order is fairly flexible, but changing it changes the emphasis.

For example:

• Sedište je slobodno. = The seat is free.
• Slobodno je ovo sedište. = This seat is free.
  This is possible, but less neutral and more marked.

So for everyday learning, Ovo sedište je slobodno is the safest and most standard version.

A very common way is:

• Da li je ovo sedište slobodno?

This is the standard yes/no question pattern:

• Da li
  • verb + rest of sentence

You may also hear:

• Je li ovo sedište slobodno?

Both are used, but Da li je... is especially common and very useful for learners.

It is pronounced approximately SEH-deesh-teh.

A few useful points:

• š sounds like English sh
• each letter is usually pronounced clearly
• Serbian spelling is very phonetic

So:

• se = seh
• diš = deesh
• te = teh

The exact stress is not marked in normal writing, but if you pronounce it clearly as SEH-deesh-teh, you will be understood.

Serbian has no articles.

So Serbian does not have separate words for:

• a seat
• the seat

The meaning comes from context or from words like ovo = this.

That is why:

• sedište can mean a seat or the seat, depending on context
• ovo sedište specifically means this seat

For English speakers, this takes some getting used to, because Serbian relies more on context than English does.

Yes, very natural.

You could hear or use it in places like:

• buses
• trains
• waiting rooms
• cinemas
• classrooms

It works well as a simple statement that a seat is available.
In real conversation, though, people often use the question form more often:

• Da li je ovo sedište slobodno?

That is probably the phrase you would use most as a learner.