Već imam rezervaciju za mali hotel blizu centra.

Već means already or by now.

In Već imam rezervaciju..., it tells you that the speaker has the reservation already, not just at some future time.

It is often placed near the beginning of the sentence for emphasis, but Serbian word order is flexible, so you may also hear things like Imam već rezervaciju...

Imam rezervaciju literally means I have a reservation, which is a very natural way to express this idea in Serbian.

Serbian can also use a verb such as rezervisati:

• Rezervisao sam sobu. = I booked a room.
• Imam rezervaciju. = I have a reservation.

The first focuses on the action of booking. The second focuses on the result: the reservation exists.

Because it is in the accusative case.

The noun rezervacija is feminine singular:

• nominative: rezervacija
• accusative: rezervaciju

Since imam takes a direct object, Serbian uses the accusative:

• Imam šta? → rezervaciju

So:

• rezervacija = reservation as the subject or dictionary form
• rezervaciju = reservation as the object

Serbian does not have articles like English a and the.

So rezervaciju could mean:

• a reservation
• the reservation

The exact meaning depends on context. In this sentence, English would usually say a reservation, but Serbian simply leaves that unspecified unless the context makes it clear.

Here za is followed by the accusative case, so:

• hotel stays hotel
• mali agrees with it and stays mali

That gives:

• za mali hotel

Literally, this means for a small hotel.

However, this is a useful place to notice a nuance: if you want to say I have a reservation at/in a small hotel, Serbian often sounds more natural with:

• Imam rezervaciju u malom hotelu blizu centra.

So the given sentence is understandable, but za mali hotel can sound a bit more like the reservation is for that hotel, rather than clearly at that hotel.

Because the adjective has to match the noun in gender, number, and case.

Hotel is:

• masculine
• singular
• here in the accusative

For masculine inanimate nouns, the accusative singular looks the same as the nominative:

• mali hotel

That is why you get mali, not malom.

You would get malom in a different case, for example:

• u malom hotelu = in a small hotel

Because blizu normally takes the genitive case.

The noun centar changes like this:

• nominative: centar
• genitive: centra

So:

• blizu centra = near the center

This is a very common pattern in Serbian:

• blizu kuće = near the house
• blizu škole = near the school
• blizu centra = near the center

Here centra usually means the city center or downtown.

So blizu centra is a very common phrase meaning:

• near the center
• more naturally in English, often near downtown or near the city center

If needed, Serbian can make this even more explicit:

• blizu centra grada = near the city center

No. Serbian word order is fairly flexible.

The sentence as given,

• Već imam rezervaciju za mali hotel blizu centra.

is natural and neutral.

But other orders are possible, with slightly different emphasis:

• Imam već rezervaciju za mali hotel blizu centra.
• Rezervaciju za mali hotel blizu centra već imam.

Putting već first gives it a slightly stronger already emphasis.

It is understandable, but many speakers would find this version more natural:

• Već imam rezervaciju u malom hotelu blizu centra.

Why? Because:

• u malom hotelu clearly means in/at a small hotel
• za mali hotel sounds more literally like for a small hotel

So the original sentence is good for learning several grammar points, but in everyday Serbian, u malom hotelu may be the more idiomatic choice for a hotel booking.