Ovaj autobus ide prema centru.

Because ovaj agrees with autobus, which is the subject of the sentence.

• autobus is masculine singular
• the subject here is in the nominative case
• so the correct form is ovaj autobus

Compare:

• ovaj autobus = this bus
• ovu ulicu = this street
• ovog vozača = this driver (in a different case)

So ovaj is the masculine singular nominative form.

In Serbian, nouns that end in a consonant are very often masculine, and autobus fits that pattern.

So:

• autobus = masculine
• singular nominative: autobus
• with a matching demonstrative: ovaj autobus

This is why you get ovaj autobus, not ova autobus or ovo autobus.

Because the subject is singular: ovaj autobus = this bus.

The verb ići means to go, and in the present tense:

• ja idem = I go
• ti ideš = you go
• on/ona/ono ide = he/she/it goes
• oni/one/ona idu = they go

Since autobus is singular, Serbian uses ide.

Prema means toward, in the direction of, or sometimes heading for.

In this sentence, it shows direction, not necessarily arrival. So the idea is:

• the bus is going toward the center
• it is headed in that direction

That is slightly different from saying it definitely goes into the center.

Because prema requires the dative case.

The base form is:

• centar = center

But after prema, it changes to the dative singular:

• prema centru = toward the center

So:

• centar = nominative
• centru = dative

This is one of the most important things to remember with prepositions in Serbian: many of them require a specific case.

Yes, prema is regularly used with the dative case.

Examples:

• prema gradu = toward the city
• prema školi = toward the school
• prema meni = toward me / according to me, depending on context

So prema centru is a very standard dative construction.

Yes, but the meaning changes a bit.

• prema centru = toward the center / in the direction of the center
• u centar = into the center / to the center

So:

• Ovaj autobus ide prema centru suggests direction
• Ovaj autobus ide u centar suggests the bus goes to the center as a destination

In everyday speech, both can work, but they are not exactly the same.

Yes, but with transportation, ide often means more than simple movement. It can mean:

• goes
• is going
• is headed
• runs or goes along this route, depending on context

So with buses, ide can describe:

1. where the bus is physically going right now
2. where that bus line normally goes

That is very natural in Serbian.

Serbian has no articles like English a and the.

So centar or centru can mean:

• a center
• the center

The exact meaning depends on context.

In prema centru, English often translates it as toward the center or toward downtown, even though Serbian does not use a separate word for the.

In a sentence like this, centar usually means the city center or downtown.

So prema centru is often understood as:

• toward downtown
• toward the city center

If the context is a town, public transport, or directions, that is the most natural interpretation.

This order is the most neutral and natural:

• Ovaj autobus = subject
• ide = verb
• prema centru = direction phrase

Serbian word order is fairly flexible, but changing it usually changes emphasis rather than basic meaning.

For example:

• Ovaj autobus ide prema centru. = neutral
• Prema centru ide ovaj autobus. = emphasis on toward the center
• Ide ovaj autobus prema centru. = possible in speech, but less neutral

So the original sentence is a very good standard model.

Yes, those are possible, but they mean different things:

• ovaj autobus = this bus
• taj autobus = that bus
• onaj autobus = that bus over there / that one further away

So ovaj is used when the bus is close to the speaker, relevant in the immediate situation, or being pointed out as this one.

A simple pronunciation guide is:

O-vai aw-to-boos ee-deh preh-ma tsen-troo

A few useful points:

• j in Serbian sounds like English y
• c sounds like ts
• u is always like oo in food
• stress is not written in normal spelling, so learners usually focus first on clear sounds

So:

• ovaj sounds roughly like ovay
• autobus = ow-to-boos
• ide = ee-deh
• prema = preh-ma
• centru = tsen-troo