Roštilj je u parku.

Because Serbian changes noun endings according to their role in the sentence. After u when it means location (in), the noun usually goes into the locative case.

So:

• park = park
• u parku = in the park

Here, parku is the locative singular form of park.

Je means is.

It is the 3rd person singular present form of the verb biti (to be).

So:

• Roštilj je... = The barbecue/grill is...

Unlike in some other Slavic languages, Serbian normally keeps this present-tense form of to be in ordinary sentences.

Because je is a clitic. In Serbian, clitics usually come in the second position in the clause.

That is why the neutral sentence is:

• Roštilj je u parku.

And also why this is possible:

• U parku je roštilj.

But putting je at the very end would sound wrong in normal Serbian.

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

So roštilj can mean:

• a barbecue / a grill
• the barbecue / the grill

The exact meaning depends on context.

If Serbian speakers want to be more specific, they can use words like:

• ovaj = this
• taj = that

But in a basic sentence like this, no article is used.

Because Serbian normally says u parku for in the park.

Prepositions in Serbian do not always match English one-for-one. Even though English sometimes uses in and sometimes at, Serbian uses u here.

So:

• u parku = in the park

Using na with park would not be the normal choice.

Not always. U can mean in or into, depending on the case that follows it.

• u parku = in the park → location, so locative
• u park = into the park / to the park → direction, so accusative

Compare:

• Roštilj je u parku. = The grill is in the park.
• Nosimo roštilj u park. = We are carrying the grill into the park.

So the case helps show whether something is already there or moving there.

Yes, Serbian word order is more flexible than English word order, because the grammar is shown partly by endings.

The most neutral version is:

• Roštilj je u parku.

But you can also say:

• U parku je roštilj.

That version puts more emphasis on where it is.

Still, the word order is not completely free, because clitics like je have placement rules.

Roštilj can mean a few related things, depending on context:

• a grill
• a barbecue
• barbecued/grilled food

In this sentence, it most naturally refers to the grill/barbecue setup being in the park, but context could shift the meaning.

This is common in Serbian: one word can cover several closely related ideas.

A rough English guide is ROSH-tilj.

Helpful sound notes:

• š sounds like sh in shoe
• lj is a soft sound, similar to the lli in some pronunciations of million, or a very soft ly

So roštilj does not sound like plain English ro-still. The last sound is softer.